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Registered:
October 2004
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THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 14:47
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I went on this bloke's blog and looked at a riddle he made,
now I'm having a major discussion with a guy that says the probability is 2/3 after monty shows you the door with the goat
APPARENTLY THE ANSWER WAS GIVEN BY A GUY WITH ONE OF THE HIGHEST IQ
well... i'm bored again... hmmm... happens so often... anyways... well don't know what I'm gonna write.. so i'll just let my fingers do the walking....
;wosaeitrnhawuoethmnlahn gliajg lkajg;kaehgflnh60awot8sdkhtjbfga.sf g.......
nah that didn't work out... I think, I'll think of someTHING thoughtful to THINK of..."Riddle Time"
okay here it goes...
You're in a Game Show called the Monty Hall Show.
Monty (The Host), presents you with 3 doors...
behind one of the doors is a Car...
The other 2 doors have a Goat behind it...
Monty knows which door the Car is in...
You are givin the chance to pick 1 door and stand in front of it...
After you choose, it is Compulsory for Monty to Pick a Door with A Goat behind it, and show you the Goat...
Monty can NEVER pick the Car...
You are left with 2 doors, and 2 Choices...
1, stay with the door you have chosen, or,..
2, switch...
What should you do? Stay? or Switch? Hmmm...
What are the odds of winning if you switch? 1/3? 2/3? 1/2? 1/1?..
NOW HERE"S THE CHAT CONVO
[R a H . R a H] says:
on your blog
[R a H . R a H] says:
there's a riddle
[R a H . R a H] says:
the "prize" is the car right?
MUSIC = LIFE says:
a huh?
MUSIC = LIFE says:
yup
[R a H . R a H] says:
and my options are to switch to the door monty isn't at or stay at the door i'm with right?
MUSIC = LIFE says:
yup
[R a H . R a H] says:
well wouldn't it be half then?
MUSIC = LIFE says:
the odds?
MUSIC = LIFE says:
nope
[R a H . R a H] says:
why's that? lol
MUSIC = LIFE says:
well....
MUSIC = LIFE says:
at first u think...
MUSIC = LIFE says:
i hav a 1 out of 3 chance
MUSIC = LIFE says:
monty opens a door with a goat...
MUSIC = LIFE says:
then u hav a 1 out of 2 chance
MUSIC = LIFE says:
when in fact u hav a 2 out of 3 chance of winning by switching and 1 out of 3 chance by staying
MUSIC = LIFE says:
its all quite confusing...
MUSIC = LIFE says:
but test it out...
[R a H . R a H] says:
why's that? monty already eliminate a possibility?
MUSIC = LIFE says:
play the game 10 times with someone... and stay.. then do it again and switch
MUSIC = LIFE says:
u'll see a big difference
MUSIC = LIFE says:
yeah its not actually a possibility....
MUSIC = LIFE says:
u'll alway hav a door opened with a goat...
[R a H . R a H] says:
isn't it a probability? because monty shows you a goat, therefore, leaving 2 doors unknown, and those 2 doors definately have 1 goat and 1 car behind them, which then concludes that you have a probability of half?
MUSIC = LIFE says:
nope....
MUSIC = LIFE says:
trust me on this
[R a H . R a H] says:
wtf? lol
[R a H . R a H] says:
can you tell me
[R a H . R a H] says:
i'm really confused! lol
MUSIC = LIFE says:
ok....
MUSIC = LIFE says:
3 doors...
MUSIC = LIFE says:
whats the probability of getting a goat?
[R a H . R a H] says:
it's like saying, if i have 10 balls, labelled 1 to 10, i take numbers 6,7,8,9,10 away, what's the probability of me choosing the number 5?
[R a H . R a H] says:
probability of getting a goat is 2/3
MUSIC = LIFE says:
ok 2 out of 3....
MUSIC = LIFE says:
right?
[R a H . R a H] says:
yeh, but can you answer my question first? lol
MUSIC = LIFE says:
which one? u hav a lot
[R a H . R a H] says:
it's like saying, if i have 10 balls, labelled 1 to 10, i take numbers 6,7,8,9,10 away, what's the probability of me choosing the number 5?
[R a H . R a H] says:
1/5 right?
[R a H . R a H] says:
isn't that question EXACTLY like your question?
MUSIC = LIFE says:
i would say
MUSIC = LIFE says:
yeah 1 of 5
MUSIC = LIFE says:
its not...
[R a H . R a H] says:
it can't be 1/10 if i choose the number 5 because i eliminated the possibility of choosing 6,7,8,910
MUSIC = LIFE says:
bcoz monty opens another door
MUSIC = LIFE says:
honestly.. if u dont believe me.... conduct a test with someone
MUSIC = LIFE says:
10x stay
MUSIC = LIFE says:
10x switch
[R a H . R a H] says:
yeh, but that test is just luck!
MUSIC = LIFE says:
no its not...
MUSIC = LIFE says:
its probability
MUSIC = LIFE says:
doing it once... its luck... doing it 10x... its probability
[R a H . R a H] says:
yeh it's a probabilty, but you saying that if i conduct a test with someone, and i do somehow prove you right or prove you wrong, the test is just base on luck
MUSIC = LIFE says:
how is it based on luck?
[R a H . R a H] says:
okay,
[R a H . R a H] says:
tell me, if i pick up 10 people from the street and ask them if their smokers, and say 8 of them are smokers, would that conclude that 8 out of 10 people are smokers in australia?
MUSIC = LIFE says:
trust me... this riddle is a famous riddle.... the answer which i told was from the a person with the highest IQ in the world
MUSIC = LIFE says:
as a minor statistic, your answer would b correct
[R a H . R a H] says:
lol it's so dumb! i'm doing probability right now in uni, and this obviously makes no sense! because monty already eliminated a factor, which then leads either right/wrong situation!
MUSIC = LIFE says:
but i'm not talking about being random....
[R a H . R a H] says:
yes it would be "correct", but highly unaccurate
MUSIC = LIFE says:
this is a literal probability....
MUSIC = LIFE says:
to the human mind and how it works, thats how it sees the situation...
MUSIC = LIFE says:
especially if you are thinking of just ONE game...
[R a H . R a H] says:
that monty situation on leaves a right/wrong answer, OKAY, if i have 3 cards, one's a jack, queen and a king, if i flip a card and show you it's a jack, what's the probability of the other two being a king? it's half because it's either a king or a queen if you choose it!
MUSIC = LIFE says:
PLUS
MUSIC = LIFE says:
theres more to it
[R a H . R a H] says:
there's more?
[R a H . R a H] says:
what you mean?
MUSIC = LIFE says:
OMG... ur not even trying to understand it
[R a H . R a H] says:
no i am... but none of it is making sense
MUSIC = LIFE says:
stop giving other examples
[R a H . R a H] says:
don't mean to offend or anything
MUSIC = LIFE says:
and let me explain
MUSIC = LIFE says:
okay...
[R a H . R a H] says:
oh okay, sorry mate
[R a H . R a H] says:
this isn't sarah btw
MUSIC = LIFE says:
it dont matter
[R a H . R a H] says:
oh okays,
MUSIC = LIFE says:
2 of 3 chance of getting a goat right?
[R a H . R a H] says:
IF monty does not reveal
MUSIC = LIFE says:
so if he reveals?
MUSIC = LIFE says:
since he ALWAYS will
MUSIC = LIFE says:
whats the chance of getting a goat?
[R a H . R a H] says:
1/2
MUSIC = LIFE says:
wrong....
MUSIC = LIFE says:
1 of 3
MUSIC = LIFE says:
y?
MUSIC = LIFE says:
okay...
[R a H . R a H] says:
yes, why
MUSIC = LIFE says:
u already know... he's ALWAYS gonna reveal a goat
MUSIC = LIFE says:
correct?
[R a H . R a H] says:
yep
MUSIC = LIFE says:
ok...
MUSIC = LIFE says:
car, goat, goat
MUSIC = LIFE says:
1, 1 ,1.....
MUSIC = LIFE says:
goat revealed....
MUSIC = LIFE says:
1, x, 1....
MUSIC = LIFE says:
look at it now....
MUSIC = LIFE says:
u hav 1 in 3, of getting a goat
[R a H . R a H] says:
the x is the car right?
MUSIC = LIFE says:
no... its a goat
[R a H . R a H] says:
oh, is the 1 suppose to represent the probability or is it to represent an unknown?
MUSIC = LIFE says:
yeah reps the probability
[R a H . R a H] says:
no no no no no no,,,,,, that's impossibile, they should all have a probability of 1/3 in that case
MUSIC = LIFE says:
wrong...
MUSIC = LIFE says:
1, 2 ,2..... 1 = car, 2 - goat
MUSIC = LIFE says:
so the prob is....
MUSIC = LIFE says:
2 of 3 is a goat
MUSIC = LIFE says:
so let start with that....
[R a H . R a H] says:
2/3 that i choose a goat IF monty does not reveal a goat, if monty reveals the goat, then it changes the probability!
MUSIC = LIFE says:
stop trying to work it out...
MUSIC = LIFE says:
my POINT is....
MUSIC = LIFE says:
from the very start... u hav a 2 of 3 chance of getting a goat...
MUSIC = LIFE says:
the next point is...
MUSIC = LIFE says:
monty ALWAYS opens a door with a goat.....
[R a H . R a H] says:
yes
MUSIC = LIFE says:
now....
MUSIC = LIFE says:
i'm
MUSIC = LIFE says:
NOT talking about doing the game only once... think 10 times
MUSIC = LIFE says:
ok....
MUSIC = LIFE says:
now.. if ur prob is 2 of 3 to get a goat....
MUSIC = LIFE says:
2 of 3 times... ur FIRST choice will be a GOAT...
MUSIC = LIFE says:
get it?
[R a H . R a H] says:
yeh
MUSIC = LIFE says:
so if u STAY... ur chance of getting a GOAT, stays at 2 of3
MUSIC = LIFE says:
but if u SWITCH, it REVERSES ur odds... making it... 2 of 3 to get the CAR
[R a H . R a H] says:
wait, has monty even revealed the door prior to this? or do we only assume that monty opens a door, but never really does?
MUSIC = LIFE says:
it wouldnt matter... bcoz not matter what... monty will ONLY open a door with a GOAT
MUSIC = LIFE says:
u hav to think latterally on this
MUSIC = LIFE says:
think about it...
MUSIC = LIFE says:
dont even think bout the car...
MUSIC = LIFE says:
think about the goats...
[R a H . R a H] says:
yeh but there's only 1 of the goat left to choose?
MUSIC = LIFE says:
OMG....
MUSIC = LIFE says:
r u thinking about 1 game or 10?
MUSIC = LIFE says:
YES theres only 1 goat to choose...
MUSIC = LIFE says:
but do u stay or switch?>??
MUSIC = LIFE says:
if u stay.... u hav a 2 of 3 chance of getting a goat
[R a H . R a H] says:
okay, if I CHOOSE 10, it will be 1/2x1/2x1/2x1/2x1/2x1/2x1/2x1/2x1/2x1/2 that i choose a goat
[R a H . R a H] says:
and the same if i choose a car
[R a H . R a H] says:
choose a car/goat ALL the time for ten times
MUSIC = LIFE says:
ur making ur own theory... i'm giving u the answer
MUSIC = LIFE says:
ur not reading it
[R a H . R a H] says:
you're giving me the answer, but your still not producing a coherant answer!
MUSIC = LIFE says:
yes i am...
MUSIC = LIFE says:
i REPEAT
MUSIC = LIFE says:
ur first choice....
MUSIC = LIFE says:
2 of 3 chance of getting a goat
MUSIC = LIFE says:
yes?
MUSIC = LIFE says:
if stay... ur chance remains at 2 of 3
MUSIC = LIFE says:
yes?
[R a H . R a H] says:
BUT HE REVEALS A GOAT ALREADY! how can i have 2/3 chance of choosing a goat after a goat is already revealed
MUSIC = LIFE says:
by STAYING u keep the odds 2 of 3
MUSIC = LIFE says:
bcoz it was ur FIRST choice and stuck with it
MUSIC = LIFE says:
it doesnt MATTER if he opens the door, its wether u STAY or switch
[R a H . R a H] says:
no if i choose, and then he reveals a goat, then i have an option of either choosing a goat or a car, but since he revealed a goat, that will change the probability of me choosing a goat/car
[R a H . R a H] says:
why doesn't it matter?
MUSIC = LIFE says:
bcoz... lets say u ONLY had 1 chance
MUSIC = LIFE says:
how would the oddds of getting a goat b
[R a H . R a H] says:
before or after a goat is revealed?
MUSIC = LIFE says:
b4
[R a H . R a H] says:
2/3
MUSIC = LIFE says:
yes
MUSIC = LIFE says:
ok...
MUSIC = LIFE says:
thats exactly the same as STAYING
MUSIC = LIFE says:
i know u hav a choice...
MUSIC = LIFE says:
stay or switch...
MUSIC = LIFE says:
now step back and think a bit....
MUSIC = LIFE says:
i'm gonna explain it one more time.. more detail
[R a H . R a H] says:
exactly, stay or switch, and after knowing that a goat is revealed. my chances of picking a goat or car is now 1/2
[R a H . R a H] says:
actually i have to go to uni tomorrow, so maybe we'll chat some other time
[R a H . R a H] says:
i really enjoyed chatting mate! lol
[R a H . R a H] says:
see ya
MUSIC = LIFE says:
sure
MUSIC = LIFE says:
see ya.. think about it
MUSIC = LIFE says:
research
MUSIC = LIFE says:
do some research and u'll realise
okay i gave up because i knew i couldn't convince him
SO WHAT DO YOU GUYS THINK?
I was on my gf's account (rah rah)
[Updated on: Sun, 28 August 2005 15:05]
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I supported Toymods
Location:
sydney.au
Registered:
August 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:06
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if you stay you have 50% probability of getting the car
if you switch its THE SAME 50% PROBABILITY BECAUSE THERE ARE ONLY 2 CHOICES!!!!!!!!
btw, that chat log is very fucking aggrivating, the person you were speaking to is a complete fuckwit.... not once do they explain 'why' the theory isnt 50/50 probability.... argh youve pissed me off
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Location:
Gold Coast
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:09
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I'd have to go with you have 1/2 chance, simply because if 1 goat has been revealed it is pretty much like a new game where instead of 1/3 chances of wining you have 1/2.
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Location:
Melbourne
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:12
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The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks the car. The game host picks either of the two goats. Switching will lose
When the player chooses a door, there is a 1/3 chance of choosing the car; there is a 2/3 chance of not choosing the car. When the host opens a door to reveal a goat, there is still a probability of 2/3 that the player has not chosen the car; knowing where one of the goats is does not change the probability of the original decision. Therefore, if the player switches to the only remaining choice, there is now a probability of 2/3 that the player has chosen the door with the car.
The odds are increased by switching
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Location:
Melbourne
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:20
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It might be easier to understand the riddle if you use 100 doors instead of 3. Say you pick a door, 99% of the time you will pick a goat, so there is a very little chance of getting it right. the host opens the next 98 doors revealing 98 goats and offers the player to open the one remaining closed door. On 99 out of 100 occasions the door the player can switch too will contain the car as 99 out of 100 times the player picked a door with a goat. Any normal human being would switch given that option.
Easy enough to understand now?
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I supported Toymods
Location:
Perth.
Registered:
April 2005
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:24
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he's a fucken idiot, its simple probability
2 options, 3 possible outcomes, take away one of those outcomes...becomes 2...
car is one of those options, goat is another...take away one of the goats, 1 car - one goat...50/50.
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Location:
Gold Coast
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 15:32
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I get the theory behind his thinking, the odds of being WRONG with your first choice is 2/3. So with your first choice you are more probable to have been WRONG. By switching you are working off the fact that their is a greater probability you were wrong the first time. If that made sense
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I supported Toymods
Location:
sydney.au
Registered:
August 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 17:42
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i think its just poorly worded with bad grammar
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 23:15
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| ShiRi wrote on Mon, 29 August 2005 01:12 |
The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks the car. The game host picks either of the two goats. Switching will lose
The odds are increased by switching
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shiri already explained this perfectly. there are three possible ways for the game to play out (and only 3). and in 2 of those you need to switch to win (giving a prob of 2/3). the problem is not with the answer, but with the guy giving it. i would say there is a 2/3 probability that this guy did not understand the answer himself and is just following what someone smarter than him had said. and confusing the shit out of people along the way.
chris
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Location:
Armidale
Registered:
January 2003
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Sun, 28 August 2005 23:51
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me = owned
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Registered:
October 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 01:17
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i think i'll go kill myself if this guy is right.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 01:30
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definitly 1/2.
can't be arsed going into an in-depth description... BabyZ has already done a pretty good job.
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Location:
Gawler, SA
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:17
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| BabyZ wrote on Mon, 29 August 2005 09:15 |
There are actually 4 possible outcomes:
The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks the car. The game host picks goat number one. Switching will lose.
The player picks the car. The game host picks goat number two. Switching will lose
2/4 chances of winning = 1/2. Changing your choice still gives you the same 50% chance of winning.
(Hey, I could be wrong, but this is my theory after 23.5 seconds of thought...)
Edit: No, I didn't read through all of the chat convo, it got too annoying 
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Not trying to be picky but shouldnt it be,
The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number one. The game host picks goat number two. Not switching will loose.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks goat number two. The game host picks goat number two. Not switching will loose.
The player picks the car. The game host picks goat number one. Switching will lose.
The player picks the car. The game host picks goat number one. Not switching will win.
The player picks the car. The game host picks goat number two. Switching will lose.
The player picks the car. The game host picks goat number two. Not switching will win.
8 possibilities, 4 chances too win, 4 chances to loose, so yes it will be still 1/2 chance.
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Location:
South Australia
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:25
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The probability is 1/2 - just because of how the game starts doesn't change how the game ends.
One door has a goat, one has a car. The other door that monty has opened doesn't matter anymore.
If you switch, you have just as much chance of winning the car as if you stay.
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:25
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nope i was right the first time. PLAYER has three choices. if the player picks the car then the hosts two choices divide that third. they do not count as different original choices.
player picks goat A, host picks goat B - 1/3 - switching wins
player picks goat B, host picks goat A - 1/3 - switching wins
player picks car, host picks goat A - 1/6 - switching loses
player picks car, host picks goat B - 1/6 - switching loses
so switching will result in a win 2/3 of the time.
sorry xolent. ive got some rope in the for sale section
 jk
chris
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I Supported Toymods
Location:
Nthn Beaches, Sydney
Registered:
October 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:33
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| Callifo wrote on Mon, 29 August 2005 12:17 |
| BabyZ wrote on Mon, 29 August 2005 09:15 |
There are actually 4 possible outcomes:
The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks the car. The game host picks goat number one. Switching will lose.
The player picks the car. The game host picks goat number two. Switching will lose
2/4 chances of winning = 1/2. Changing your choice still gives you the same 50% chance of winning.
(Hey, I could be wrong, but this is my theory after 23.5 seconds of thought...)
Edit: No, I didn't read through all of the chat convo, it got too annoying
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Not trying to be picky but shouldnt it be,
The player picks goat number one. The game host picks goat number two. Switching will win the car.
The player picks goat number one. The game host picks goat number two. Not switching will loose.
The player picks goat number two. The game host picks goat number one. Switching will win the car.
The player picks goat number two. The game host picks goat number two. Not switching will loose.
The player picks the car. The game host picks goat number one. Switching will lose.
The player picks the car. The game host picks goat number one. Not switching will win.
The player picks the car. The game host picks goat number two. Switching will lose.
The player picks the car. The game host picks goat number two. Not switching will win.
8 possibilities, 4 chances too win, 4 chances to loose, so yes it will be still 1/2 chance.
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Yep, probability is 0.5
The probability that guy is a knob is 1.0 Answer from someone with highest IQ in the world?? Smarter than this guy doesn't make you a genius.
Shiri, you helped me understand what the guy is trying to explain, but you actually ended up proving the 0.5 reasoning. You have to make 2 choices, but it all comes down to the last one, between either right or wrong, switch or don't. No matter what you pick the first time, you always have to make a 2nd pick between the car or a goat, and there's no greater probability picking one than the other.
1 out of 2 = 1/2 = 0.5
(It's actually 3 out of 6 possible outcomes = 3/6 = 0.5;
car, then switch/stay, goat 1 then switch/stay, and goat 2 then switch/stay)
GT
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Location:
Armidale
Registered:
January 2003
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:40
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gt
prob of wining is 50%
but that was not the question
using your 6 possible outcomes
car - switch - lose
car - dont switch - win
goat A - switch - win
goat A - dont switch - lose
goat B - switch - win
goat B - dont switch - lose
you can see that switching results in a win 2 out of 3 times
and not switching wins 1 out of 3 times
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Location:
South Australia
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:41
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Just do it the laborious way - look at all the possible ways the game can play out, then look at how often switching nets you a win - and i think you'll find that it's 1/2 the time.
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Location:
Gawler, SA
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:51
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| mynameisrodney wrote on Mon, 29 August 2005 12:10 |
car - switch - lose
car - dont switch - win
goat A - switch - win
goat A - dont switch - lose
goat B - switch - win
goat B - dont switch - lose
you can see that switching results in a win 2 out of 3 times
and not switching wins 1 out of 3 times
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From that we see its switch wins 2/6 times and not switching wins 1/6 times. With another 3/6 combinations in between.
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:54
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sorry shiri but i'm stealing your idea to explain it.
say there were 100 doors.
you would pick a goat 99% of the time meaning that the other door would be the car 99% of the time and so switching would win 99% of the time.
revealing the goat really gives no new information. you already KNOW that there is 2 goats. you already know that the host WILL reveal a goat. so when he opens the door with the goat why should the prob that you chose the car suddenly jump to 1/2. like any good riddle it is misdirecxtion which causes the confusion. revealing the other goat has no effect on the probability that you chose the car.
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Location:
Melbourne - NthSubs
Registered:
January 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 02:58
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I Supported Toymods
Location:
Nthn Beaches, Sydney
Registered:
October 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 03:04
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Ah shit. Looks like i misread the question (could've been clearer, grrr...)
I've been arguing chance of winning, he's asking chance of switching winning.
Switching and winning occurs 2 times out of 6 possible outcomes.
Probability = 1/3 (or 0.333333.....)
Price goes to Callifo for finally getting it straight 1st. Damn using my rusty brain...
GT
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Location:
Melbourne - NthSubs
Registered:
January 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 03:16
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maybe if u used ur ears, listen for goat sounds for a few moments and pick the door with no goat sounds!?!... 
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Location:
South Australia
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 03:22
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I think I understand why this all causes confusion. One way to look at things is to look at all the way the game can play out - giving the impression that if you are standing in front of a car, when monty chooses Goat A the game is somehow different from if he chooses Goat B.
Basically - it works out to 2/3rds chance of winning if you switch.
At the start of the game you have three options.
There is a 2/3 chance you are standing in front of a goat.
When you switch you win a car.
If you don't switch you lose.
There is a 1/3 chance you are standing in front of a car.
When you switch you lose, if you don't switch you win.
Work the rest out.
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Location:
South Australia
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 03:36
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I think it's best if you look at what the chances of loosing are. Like with the example, if there are a 100 doors, and 99 of them contain goats. You would duly pick a door saying to yourself
"There is a 99% chance I have just picked a goat"...so the host goes and does his thing opening up all the other doors showing a bunch of goats (goat overload by now).
You are standing infront of a door that you are 99% sure contains a goat.
What should you do?
SWITCH!
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Location:
Sydney
Registered:
June 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 09:52
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Argh. MY mind!!!  But I have to just say that the probability is 1/2, not 2/3
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Location:
Kellyville, Sydney
Registered:
June 2004
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Location:
Pine Rivers QLD
Registered:
April 2005
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Re: THE STUPIDEST RIDDLE EVER!!
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Mon, 29 August 2005 22:52
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| rthy wrote on Mon, 29 August 2005 13:16 |
maybe if u used ur ears, listen for goat sounds for a few moments and pick the door with no goat sounds!?!...
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wouldn't it just be easier to pick the door making motor noises
I will have to agree with the 1/3. otherwise they would just have 2 doors. There would have to be a reason for picking a door before your shown a goat, otherwise if the chance is a constant then it would be pointless having 3 doors in the first place.
It is easier (as some people have) to not look at the problem of winning a car, but looking at the problem as the chance of getting the car if you switch.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Location:
Canberra
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:25
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| Quote: |
After you choose, it is Compulsory for Monty to Pick a Door with A Goat behind it, and show you the Goat...
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We all assumed that he has to choose a different door than you... this version of the ridlle never says this. The published version does.
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:31
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| Quote: |
car - switch - lose
car - dont switch - win
goat A - switch - win
goat A - dont switch - lose
goat B - switch - win
goat B - dont switch - lose
you can see that switching results in a win 2 out of 3 times
and not switching wins 1 out of 3 times
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cruzida, seeing as you are wrong i wouldn't go around calling everyone else idiots.
squid, i'm not sure what you are trying to say.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:32
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You want to prove to me why I'm wrong instead of quoting shit?
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Location:
Canberra
Registered:
August 2003
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:41
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that was a quote by ME stating all possible outcomes.
acording to your logic the odds are 50/50 because you either win or you lose.
but in a similar situation:
tonight i will either:
a) bone imogen bailey
or
b) not bone imogen bailey
still only two possible outcomes. now i really wish that there was a 50/50 chance for me there, but somehow i doubt it  .
as in my above posts there are 6 possible ways to play the game
car + switch = lose
goat A + switch = win
goat B + switch = win
car + stay = win
goat A + stay = lose
goat B + stay = lose
so switching results in a win 2/3 of the time and staying results in a win 1/3 of the time.
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Location:
Canberra
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:43
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| mynameisrodney wrote on Tue, 30 August 2005 12:31 |
squid, i'm not sure what you are trying to say.
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Because of the bad grammar in this version of the riddle there is no restriction on monty opening the door you are standing in front of.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 02:57
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It all depends which part of the story you take the odds from.
From the start of the story, yes, its as you said.
But if you look at end of the story, the odds have changed.
One of the doors has been removed.
So Door A is a win, Door B is lose.
Or Door B is a win, Door A is lose.
(Presuming Door C has been opened).
When the host opened a door, the odds changed from 1/3 to 1/2.
Me personally, I take the odds from the end of the story, because that is where the question is asked.
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:01
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but you already knew there was another door with a goat behind it. no new information is gained when the door is opened. the odds do not change at all.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:05
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rodney - please tell me you dont study accounting or actuarial 
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:11
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nope computer/biomedical engineering
i have done stats
i am right on this, check the link that squid posted if you are not sure. i cant think of any way to explain it more simply than this:
| Quote: |
car + switch = lose
goat A + switch = win
goat B + switch = win
car + stay = win
goat A + stay = lose
goat B + stay = lose
so switching results in a win 2/3 of the time and staying results in a win 1/3 of the time.
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the OVERALL chance of winning is 50/50. but that is not the question. the question is:
What is the chance of winning IF YOU SWITCH?
as you can see above out of the 3 possible outcomes that involve a switch 2 of them result in a win. therefor, odds of winning if you switch = 2/3.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:12
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| mynameisrodney wrote on Tue, 30 August 2005 11:01 |
but you already knew there was another door with a goat behind it. no new information is gained when the door is opened. the odds do not change at all.
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Yes they did.
He offers a switch, which means the game basically starts again, but this time, with 2 doors.
If there was no switch, it would be 1/3, but there was a switch.
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Location:
Melbourne
Registered:
November 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:50
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... I'm doing a bloody experiment on this...
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Location:
South Australia
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 03:55
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| Quote: |
He offers a switch, which means the game basically starts again, but this time, with 2 doors.
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bzzt wrong. The game would 'start all over again' but you have to also carry on the probability of what door you are already standing at. Once you get it it's so simple.
There are two doors left, one has a car and one has a goat. You are standing in front of one door already. If you switch what are the odds of standing in front of the car? The easiest way to look at it is what are the odds you are standing in front of a goat at the 'start' of the 'new game'.
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Location:
Sydney
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:02
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I'm with Rodney.
2/3s here.
I might see if I can do it on paper or write a quick program to test it.
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I supported Toymods
Location:
Australia
Registered:
November 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:19
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| RWDboy wrote on Tue, 30 August 2005 11:55 |
| Quote: |
He offers a switch, which means the game basically starts again, but this time, with 2 doors.
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bzzt wrong. The game would 'start all over again' but you have to also carry on the probability of what door you are already standing at. Once you get it it's so simple.
There are two doors left, one has a car and one has a goat. You are standing in front of one door already. If you switch what are the odds of standing in front of the car? The easiest way to look at it is what are the odds you are standing in front of a goat at the 'start' of the 'new game'.
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You said I was wrong, and then went on to agree with me...
I'm still standing by the fact that as soon as one door was proved wrong, and you were offered to rethink your decision, the odds changed, in your favour.
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Location:
Sydney
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:39
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I didn't wite code to display the host's choice as it can be assumed. I put it into the results manually so it was more transparent.
The cut and paste stuffed up my indentation.
class test
{
public static void main(String[] args)
{
int win = 0;
int total = 0;
int choice = 1;
int carDoor = 1;
System.out.println("Car, Choice, Host");
while (carDoor <= 3)
{
choice = 1;
while (choice <= 3)
{
total++;
if (carDoor != choice) {
System.out.println(carDoor + " , " + choice + " , win");
win++;
} else {
System.out.println(carDoor + " , " + choice + " , ");
}
choice++;
}
carDoor++;
}
System.out.println("Total = " + total);
System.out.println("Wins = " + win);
}
}
Car, Choice, Host
1 , 1 , 2
1 , 2 , 3 win
1 , 3 , 2 win
2 , 1 , 3 win
2 , 2 , 1
2 , 3 , 1 win
3 , 1 , 2 win
3 , 2 , 1 win
3 , 3 , 2
Total = 9
Wins = 6
Press any key to continue . . .
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Location:
Kellyville, Sydney
Registered:
June 2004
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:47
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hey supraPete, mine is bigger than yours.
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Location:
Sydney
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:50
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| mynameisrodney wrote on Tue, 30 August 2005 14:47 |
hey supraPete, mine is bigger than yours.
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Then you need to learn how to write better code
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 04:53
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i was trying to make a tidy IO with random choices for the host, not a mathematical proof like yours.
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Location:
Brisbane
Registered:
May 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 05:44
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Ok... let's get this straight. The entire contention here is do to with the wording of the question.
The question states "what is the chance of winning by SWITCHING?". The answer is 2 out of 3, exactly how Shiri explained it directly after the first post (working of course on the assumption that if you initially pick the car, switching is no longer and option). Allowing for the complete moron who still decides to switch after he has already won the car, the answer is 1 out of 2.
However, RAH RAH and several people here are answering their own question, "what is the chance of winning?". Of course the answer to this question is 1 out of 2, because your first choice really has nothing to do with your second choice. There is nothing that differentiates between the two goats, who cares which one the host picks.
MUSIC = LIFE is really the idiot here because he failed to see that they were both on completely different wavelengths.
Oh yeah, I hate these questions so bad! How many marks have I lost on multiple choice tests because of some gay F**KED up wording!
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 05:50
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now you have gone and confused the matter. you dont know whether or not you have picked the car so switching is still an option.
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Location:
Sydney
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 06:35
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| white86 wrote on Tue, 30 August 2005 15:44 |
(working of course on the assumption that if you initially pick the car, switching is no longer and option). Allowing for the complete moron who still decides to switch after he has already won the car, the answer is 1 out of 2.
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NO. You've assumed wrong.
In this example (car and goat example) the ONLY option is to switch. ie. you MUST switch if you had picked the car or not.
We were trying to work out what the probability of winning when you MUST switch. Thats the point of the riddle.
I'm waiting for someone to bring proof (or "fix" my code) which will show that it is 1/2 not 2/3.
Maybe we should start another post of "who has the highest IQ" or "who can call someone else an idiot or moron when they're wrong".
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Location:
Kellyville, Sydney
Registered:
June 2004
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 06:46
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notice how everyone that said 1/2 has now disapeared off the face of the planet
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Location:
Gawler, SA
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 07:02
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People that were saying 1/2 were talking about win/loose not chance of winning by switch/not switch.
I still stick by my other numbers though by if you switch you have 1/3 chance of winning, if you dont switch you have 1/6 chance of winning, and 1/2 chance of win/loosing by other combinations. So it would yes be better to switch.
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Location:
Sydney
Registered:
July 2002
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 07:04
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| Callifo wrote on Tue, 30 August 2005 17:02 |
I still stick by my other numbers though by if you switch you have 1/3 chance of winning, if you dont switch you have 1/6 chance of winning, and 1/2 chance of win/loosing by other combinations. So it would yes be better to switch.
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Can I make this my signature?
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Location:
Armidale
Registered:
January 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 07:39
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| mynameisrodney wrote on Tue, 30 August 2005 16:46 |
notice how everyone that said 1/2 has now disapeared off the face of the planet
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Nah, we just can't be bothered arguing because we know that we are right, and that the rest of the fµ˘kwits have no clue.
Just kidding  . I think it depends more on the wording of the question, and on which question you are actually answering.
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Location:
Gawler, SA
Registered:
August 2003
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Re: THE STUPIDEST RIDDLE EVER!!
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Tue, 30 August 2005 07:44
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After finding the proper maths behind it, I have to admit it, we are wrong.
| Quote: |
P[A|B] = Pr[A and B]/P[B]
Take a typical situation in the game. Suppose the contestant has chosen Door 3 and Monty Hall reveals that there is a goat behind Door 2. Let us compute the conditional probability that the car is behind Door 1. Let A stand for the condition that there is a car behind Door 1 and the contestant has chosen Door 3. Let B stand for the condition that Monty Hall has revealed that there is a goat behind Door 2 given that the contestant has chosen Door 3. The probability of A and B ( P[A and B] ) is just (1/3)(1/3)=1/9 because if the car is behind Door 1 and the contestant has chosen Door 3 it is 100 percent certain that Monty Hall will show what is behind Door 2. The problem is the computation of the probability of being shown a goat behind Door 2 given that the choice was Door 3. This situation can arise in two ways. One, when the car is behind Door 1 and another when the car is behind Door 3. The first way has a probability of 1/9, as has already been computed above. In the second way, the host could reveal either what is behind Door 1 or Door 2. If he is equally likely to choose either of these doors then the prob ability of the second way is (1/2)(1/9). Therefore the probabil ity of there being revealed a goat behind Door 2 when the con testant has chosen Door 3 is
(1/9) + (1/2)(1/9) = (3/2)(1/9).
This is the probability of B; i.e., P[B].
The conditional probability we want, P[A|B], is given by
P[A|B] = P[A and B]/P[B] = (l/9)/(3/2)(1/9) = 2/3.
This means that the conditional probability that the car is behind Door 3 given that the contestant has chosen Door 3 and has been shown that there is a goat behind Door 2 is only l/3. Therefore it is worthwhile to switch.
This other conditional probability can be calculated either as
1 - P[A|B],
or from the probability the car is behind Door 3 given that the contestant has chosen Door 3 and has been shown a goat behind Door 2. This latter probability is (1/3)(1/3)(1/2) so when it divided by P[B] one gets l/3.
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Location:
Melbourne
Registered:
November 2003
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go figure.