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Subject: Re: The Computer-Chess Player And The Mathematician (was: Waltzing Matilda

Author: Serge Desmarais

Date: 20:30:44 08/28/98

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On August 18, 1998 at 07:26:14, fca wrote:

ut I didn't answer (c).

>I already gave an example of a *bad question* (I repeat, with some
>simplification):
>
>Given: A child may be only a boy (B) or a girl (G). Twins and higher do not
>occur.  Bs and Gs are equiprobable.  The sex of any existing child does in no
>way affect the probability of the sex of its later-born sibling or half-sibling
>being B or G.
>A man has exactly two biological children.
>Question (1): "One of them is a B. What is the probability that both are Bs?"
>Question (2): "The older of them is a B. What is the probability that both are
>Bs?"
>
>Now the answer to (1) is 1/3, and to (2) is 1/2.



   I don't understand how you can say that the answer to 1 is 1/3? If the first
one is a boy, the other child has 50% chance of being a boy and 50% of being a
girl, so that should be 1/2, instead!


Serge Desmarais




>
>In computer-chess
>
>Kind regards
>
>fca
>
>PS: Yes I can count.  The mathematician was a woman.
>
>;-)



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