🚀 go-pugleaf

cmh@eng.cam.ac.uk (C.M. Hicks) writes:

>karr@cs.cornell.edu (David Karr) writes:

>>>You meet the daughter of a friend of yours on the street.  You know
>>>that your friend has two children.  You think to yourself, "Ignoring
>>>the occurrence of twins, and sex-linked differences in birth rates
>>>and infant mortality, what are the odds of this girl's sibling also
>>>being a girl?"

>One half - The probability of the other child being a girl is totally
>independent of the sex of the first. The first child being
>a girl does affect the 50-50 boy-girl distribution of the second (or any 
>other) child.

Of course, you could say that the possible permutations for a two-child
family are:

        Male    Female
      Female    Male
      Female    Female
        Male    Male

These all have probability 1/4, and since one child is female, one permutation
is discounted (male-male), giving a final probability of a third...

Heck - flame war ahead, and all in my own mind - do I believe Bayes Theorem?

Christopher Hicks

--
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 Christopher Hicks    |    If it doesn't fit...
 cmh@uk.ac.cam.eng    |                        ...you need a bigger hammer.
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