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Subject: Re: New and final solution of the Monty Hall Dilemma

Author: Gerrit Reubold

Date: 13:17:02 09/27/02

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On September 27, 2002 at 16:04:45, Uri Blass wrote:

>On September 27, 2002 at 15:40:07, Gerrit Reubold wrote:
>
>>On September 27, 2002 at 15:04:26, Uri Blass wrote:
>>
>>>On September 27, 2002 at 14:40:09, Gerrit Reubold wrote:
>>>
>>>>Uri,
>>>>
>>>>I think your model of the game is not a model of the situation which I am
>>>>discussing.
>>>>
>>>>Suppose you and me are playing the following game (f.ex. by email).
>>>>
>>>>1. I, the host, take an empty chessboard and put a single king one one of the
>>>>squares. Trust me that I don't cheat. You send me your guess which square this
>>>>might be.
>>>>
>>>>2. I assume you, the candidate, guess it is a1.
>>>>
>>>>3. I give you a hint:
>>>>The square is not one of
>>>>   b1 c1 d1 e1 f1 g1 h1
>>>>a2 b2 c2 d2 e2 f2 g2 h2
>>>>a3 b3 c3 d3 e3 f3 g3 h3
>>>>a4 b4 c4 d4 e4 f4 g4 h4
>>>>a5 b5 c5 d5 e5 f5    h5
>>>>a6 b6 c6 d6 e6 f6 g6 h6
>>>>a7 b7 c7 d7 e7 f7 g7 h7
>>>>a8 b8 c8 d8 e8 f8 g8 h8
>>>>
>>>>(Note that it is no difference if I suddenly forgot on which square the king
>>>>stands, I decide to look only on the given 62 squares and, surprise, all of them
>>>>are empty.)
>>>
>>>It is important if you know where the king is.
>>
>>No.
>>
>>>
>>>Suppose for the discussion that you also do not know where the king is
>>>so you always expose all the squares except a1 g5 after
>>>I choose a1.
>>
>>No. I look at 62 random squares, excluding a1.
>>
>>>
>>>Suppose that we start to play 64000 games(most of them are
>>>not played because you discover the king
>>>in one of the 62 squares).
>>
>>No. We play only this single game. We might play again and my hint will likely
>>be different, maybe all squares except a1 and f8.
>>
>>Do you think it is a difference whether I forgot where the king is (I would have
>>told you "game over" if I accidently looked at a square with the king on it) or
>>whether I know the square of the king.
>
>Yes
>Suppose you do not know the square of the king.
>
>Suppose that for every square x(not a1) we play 64000 games when you choose
>square x.
>In these games the king is in square y in 1000 games for every square y.
>
>I claim that I can expect 62000 games out of every 64000 games to be canceled
>because the king is exposed(not in x and not in a1).
>
>I expect to win 1000 games out of 64000 games(the 1000 games when the king is in
>a1) and I expect to lose 1000 games out of 64000(the 1000 games when the king is
>in square x).
>
>The same hapen for everyone of the 63 squares that you can choose and I expect
>to win 63000 games and to lose 63000 games.
>
>Uri

One question:

Do you agree: If the host knows the solution (the door with the car, the
position of the king, ...), the candidate should switch?

Greetings,
Gerrit



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