Monty Hall Dilemma - Winning a GTI on a Game Show

**team_v** · 17-03-2010, 07:41 AM

Originally Posted by Timbo

The host opens a door, revealing a goat. Previously, that door had a 1 in 3 chance of hiding the car, but it didn't. It had a 2 in 3 chance of hiding a goat, it did, BUT IT WASN'T A RANDOM CHOICE by the host.

Critical to the logic here is that the host is always going to pick a door hiding a goat. IT IS NOT A RANDOM CHOICE, it is a game.

The issue I have is that since the host is always going to reveal a goat, why bother even including that information/door in the scenario since it will never be the car and hence, removes 1 door from your next choice, resetting the statistical probablility of one of the remaining 2 doors holding the gti to 50/50.
The host may have known but your choice was still random and the statistics then say you have a 50/50 chance.

1 door has been revealed and has a goat.
2 doors remain, 1 (goat) and 1 (GTI). (statistics will reset due to the fact there are now only 2 choices)
50:50 chance.

Yes originally the chances of your door were 1/3 however a door has been revealed, removed from your choice (if you want the GTI) and thus you only have 2 doors remianing so the 1/3 chance is no longer valid as there is only 2 doors you would logically choose from.

However, we can all rest happily in the knowledge that no matter what choice we make, one of the 3 eventualities that split off from this scenario will win the GTI so we will have won in some alternate universe if we don't win in this one.

Also take note that most game show hosts will try to make you choose another option anyway if you are going for a big prize (see who wants to be a millionaire and all that)
They only help you out when the prize pool is quite small.

**Timbo** · 17-03-2010, 10:13 AM

I give up!

**Flighter** · 17-03-2010, 01:36 PM

Originally Posted by Timbo

I give up!

I'm not surprised. This is so obvious from both the video and diagrams that people have posted, plus the multiple explanations that this is not a case of random probability. Heck the only reason it is so interesting is *because* it seems counter-intuitive.

Of course this is also easy enough to try at home, yet I bet there are those among the disbelievers who probably won't do this because they deep down they know they will be found to be incorrect and are afraid to admit as much, even if only to themselves. John F. Kennedy's ratings in the political opinion polls *rose* after he admitted to the public that he blew it with the Bay of Pigs fiasco, but not everyone understands that it's okay to be human and hence be wrong sometimes.

**Buller_Scott** · 17-03-2010, 02:02 PM

you're being way too presumptuous.

it's not about ''being the big man, being humble, being honest", nor about being "terrified" to admit that someone on the other side of the fence may be right.

no to claim, but i did 4 unit maths in year 11/12. that was 13 hours of math classes a week BEFORE homework/ study/ assignments. i KNOW probability, and any comprehensive mathematical explanations in this thread are REAL, and CANNOT be disproved by some playing cards from the local $2 shop. my explanations have a basis in mathematics, in mathematical probability.

i am only too willing to admit that my earlier explanations were somewhat presumptuous as i had neglected the vital fact that the game was rigged by way of the host's intention to reveal a goat behind the first door, and that that fact lends itself somewhat as an odd in the contestant's favor, should you be determined to treat progression of time throughout the gameshow as static, and mutually exclusive to the progression of the opening of doors.

in the same way that the proponents for the 50/50 argument may be ''afraid to admit'' whatever it is we should be admitting, the proponents for ''2/3'' seem to be ''afraid'' to explain just how a game show's events can proceed when time is not?

**Spilledprawn** · 17-03-2010, 05:10 PM

Originally Posted by Buller_Scott

no to claim, but i did 4 unit maths in year 11/12. that was 13 hours of math classes a week BEFORE homework/ study/ assignments. i KNOW probability, and any comprehensive mathematical explanations in this thread are REAL, and CANNOT be disproved by some playing cards from the local $2 shop. my explanations have a basis in mathematics, in mathematical probability.

i?

It's interesting you place so much value on "mathematical probability" above "some playing cards" when the cards will actually prove the reality

Okay, before we start the game we know with absolute conviction that out of the 3 doors, one has a car and two have goats.
We make our choice of the doors - and have a 2/3 chance of picking a goat
We know that of the two remaining doors - at least one will have a goat.
We know that the host will reveal a goat, it doesn't matter which one of the two remaining doors that goat is behind, we already know it exists, and knew it when we made our original decision. We are therefore better off switching.

IF the host revealed that OUR DOOR had a goat and invited us to change, then our chances are resolved to 50/50 (only this removes the dependancy of the original choice)

If the host doesn't open any doors at all, and you're invited to change, the chance remains 1/3

Please try it with a set of cards, it will only take a few minutes. It isn't magic, it is just maths.

**schoona** · 17-03-2010, 07:00 PM

http://www.youtube.com/watch?v=7SjFJImg2Z8

**Buller_Scott** · 17-03-2010, 07:17 PM

[QUOTE=Spilledprawn;478589]

IF the host revealed that OUR DOOR had a goat and invited us to change, then our chances are resolved to 50/50 (only this removes the dependancy of the original choice)

[QUOTE]

isnt that precisely what happens in this particular scenario, that the host knowingly selects the first door to be opened as one which houses a goat, THEN he asks if you want to switch?

a couple of thread pages ago, there was some discussion in which the function of the host was established as intentionally opening a door which he knew housed a goat, before asking the contestant if he wants to switch.

**cme2c** · 17-03-2010, 07:42 PM

[QUOTE=Buller_Scott;478661][QUOTE=Spilledprawn;478589]

IF the host revealed that OUR DOOR had a goat and invited us to change, then our chances are resolved to 50/50 (only this removes the dependancy of the original choice)

isnt that precisely what happens in this particular scenario, that the host knowingly selects the first door to be opened as one which houses a goat, THEN he asks if you want to switch?

a couple of thread pages ago, there was some discussion in which the function of the host was established as intentionally opening a door which he knew housed a goat, before asking the contestant if he wants to switch.

I, too did 4 Unit maths. My wife has done statistics to 3rd year university. Yet she still plays poker machines. I have given up pointing this out, as I dislike pain.

Anyhow, the probabilities are fixed with the contestants choice. Whatever the choice, the host can open a door which hides a goat. It is obfuscation. Smoke and mirrors. 3 card monte.

On the subject of theory and practice.

An engineer and a physicist, both male and heterosexual, are placed at one goal line of a football field. At the other goal line opposite each is a naked, desireable woman.

They are each told that a whistle will sound. At each whistle, thay can move half the distance to the other end of the field. Each time they can halve the distance again, and so on.

So assuming a 100m field, you would be 50, then 75, then 87.5 m and so on.

The whistle blows. The physicist doesn't move. The engineer runs to the half way line. The physicist explains that as he can only halve the distance each time, he can never reach the other goal line. The engineer is given this information, agrees, but says "I can get close enough".

Try it with $2 shop cards. The Monty Hall problem, that is.

**schoona** · 17-03-2010, 07:57 PM

[QUOTE=cme2c;478679][QUOTE=Buller_Scott;478661]

Originally Posted by Spilledprawn

IF the host revealed that OUR DOOR had a goat and invited us to change, then our chances are resolved to 50/50 (only this removes the dependancy of the original choice)

I, too did 4 Unit maths. My wife has done statistics to 3rd year university. Yet she still plays poker machines. I have given up pointing this out, as I dislike pain.

Anyhow, the probabilities are fixed with the contestants choice. Whatever the choice, the host can open a door which hides a goat. It is obfuscation. Smoke and mirrors. 3 card monte.

On the subject of theory and practice.

An engineer and a physicist, both male and heterosexual, are placed at one goal line of a football field. At the other goal line opposite each is a naked, desireable woman.

They are each told that a whistle will sound. At each whistle, thay can move half the distance to the other end of the field. Each time they can halve the distance again, and so on.

So assuming a 100m field, you would be 50, then 75, then 87.5 m and so on.

The whistle blows. The physicist doesn't move. The engineer runs to the half way line. The physicist explains that as he can only halve the distance each time, he can never reach the other goal line. The engineer is given this information, agrees, but says "I can get close enough".

Try it with $2 shop cards. The Monty Hall problem, that is.

You only move half the distance yes, but the 100m is a finite point, therefore you will reach it.