oldy but a goodie: there are 3 doors.

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Mar 5, 2012
2:53:05pm

johnnycarson

oldy but a goodie: there are 3 doors.

there is a new car behind one of the doors. the host of our little game, who knows where the car is, asks you to guess one of the doors. let's say that you guess door C. the host then opens door A and shows you that the car is not behind door A. should you then switch your guess to door B?

yes. you should. don't ask me why.

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johnnycarson

Bio page: johnnycarson
Joined: Nov 21, 2005
Last login: Jan 17, 2022
Total posts: 92,585 (10,302 FO)

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Messages

Author

Time

oldy but a goodie: there are 3 doors.

3/5/12 2:53pm

I know why. It's basic math.

brj8

3/5/12 2:53pm

Yes, switch. Your odds double.

chago04

3/5/12 2:53pm

Yup.

brj8

3/5/12 2:54pm

Depends on what school of thought you belong to.

chago04

3/5/12 2:55pm

That's a fun probability problem

3/5/12 2:54pm

Original odds are 1/3, but upon being

chago04

3/5/12 2:56pm

Yes - that's it

3/5/12 2:58pm

We discussed it a lot in Stat 441 with Tolley.

chago04

3/5/12 2:59pm

Read about the Monty Hall problem on wikipedia:

benny1982

3/5/12 2:54pm

Test the probability of the MH problem at this link:

benny1982

3/5/12 3:03pm

Cool. Learn something new everyday.

Oregano

3/5/12 3:11pm

I just did 10 of each. My results:

workindev

3/5/12 3:18pm

Mine:

BYU-Texas

3/5/12 3:26pm

You should change your choice. I don't know why but

scottfunkel

3/5/12 2:54pm

i think its because the girl was hot.

3/5/12 2:54pm

Mythbusters did an episode on this.

Pwride

3/5/12 3:01pm

<< Deleted >>

ds7

3/5/12 3:02pm

you don't add, the kid spent the $2 on cigarrettes in the

3/5/12 3:05pm

Do your odds of being right change without switching?

scall

3/5/12 2:58pm

No - your odds were 1/3 and are still 1/3

Cougar-Duck

3/5/12 2:59pm

Why don't the odds change?

scall

3/5/12 3:01pm

I may not get it, but I don't believe the 1/3 against 2/3

'dweller

3/5/12 3:03pm

there are a lot of smart people who think it's 50/50

The Shazad

3/5/12 3:09pm

Think of it this way

Mems

3/5/12 3:04pm

The same could be said for door number 2

'dweller

3/5/12 3:10pm

This is what I think as well.

scall

3/5/12 3:11pm

All that matters is your initial chance to choose right or

Bainge

3/5/12 3:13pm

I'd agree if you didn't have a 2nd chance to alter the

scall

3/5/12 3:17pm

Is this metaphysics? Where we create our own reality??

'dweller

3/5/12 3:21pm

The outcomes aren't weighted evenly

Mems

3/5/12 3:24pm

Imagine there were 100 doors

The Shazad

3/5/12 3:28pm

So there is an assumption of a bias in the host

'dweller

3/5/12 3:46pm

no. the only assumption is that the host knows where the car

3/5/12 3:49pm

^^^this^^^^

Mems

3/5/12 3:54pm

exactly

The Shazad

3/5/12 3:57pm

But that is the bias, that he will never show you

'dweller

3/5/12 4:24pm

that's part of the problem statement

The Shazad

3/5/12 4:27pm

Right, that's the human bias

'dweller

3/5/12 4:38pm

Just thinking it through... if the host

'dweller

3/5/12 4:47pm

yes, if his pick is completely random

The Shazad

3/5/12 4:57pm

Another way to think about it

Mems

3/5/12 3:18pm

Just bleat out a goat call and wait for a response

3/5/12 3:37pm

there are 9 possible combinations

The Shazad

3/5/12 3:19pm

shazad wins the day. read this ^^^^. i don't remember

3/5/12 3:48pm

An explanation that everyone can undertsnad

jdart

3/5/12 4:39pm

good guesses - not quite

The Shazad

3/5/12 4:52pm

think of it this way....

The Shazad

3/5/12 3:06pm

I understand the theory, I just don't see how it doesn't

scall

3/5/12 3:07pm

This is the best way to visualize it

workindev

3/5/12 3:08pm

here's another old one...

ds7

3/5/12 3:03pm

Shouldn't you subtract the $2 instead of adding it?

workindev

3/5/12 3:06pm

Yep. Gets it to $25 bucks for the room.

BYU-Texas

3/5/12 3:08pm

I haven't heard this one. Care to answer?

PharmCoug

3/5/12 3:09pm

They each paid $9 ($27 total) for a $25 room

workindev

3/5/12 3:11pm

Yep. The setup to the question is smoke and mirrors designed

benny1982

3/5/12 3:12pm

Yep, They paid for Room and tip. 25/3 + 2/3 each

BYU-Texas

3/5/12 3:13pm

got it now, thanks.

PharmCoug

3/5/12 3:16pm

Whoa. I don't get it at all.

CrackerJack

3/5/12 3:26pm

they trick you by making you think you are adding to 30.

LeFleur

3/5/12 3:28pm

Oh. I get it now. Thanks! I feel smart now.

CrackerJack

3/5/12 3:30pm

Right, the price is no longer $30, it is now $25

workindev

3/5/12 3:32pm

which one has the car ? C or B?

LeFleur

3/5/12 3:17pm

also, if we find out its not a, wouldn't it switch to 50/50?

LeFleur

3/5/12 3:20pm

There is a 50/50 chance for each of the remaining doors

workindev

3/5/12 3:28pm

+1000000 that makes perfect sense. Thanks!

LeFleur

3/5/12 3:30pm

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