You're quite right, Andy. I think I've seen this puzzle stated incorrectly more often than stated correctly; it's hard to say it right. But if you walk up to the house of a family which you know has two kids and there's a girl playing in the yard, the probability that her sibling is a girl is indeed 1/2, not 1/3. "The child playing outside" has distinguished the two kids. I'm surprised; Dennis Shasha is usually more careful than that. --Michael Kleber On 6/12/06, Andy Latto <Andy.Latto@gensym.com> wrote:
I think the solution to the last of the probability puzzles on the Scientific American web site at http://www.sciam.com/article.cfm?chanID=sa010&articleID=000E3F5B-04C7-1270-8 4C783414B7F0000 is incorrect.
But since this sort of puzzle is notoriously tricky to get right, I thought I'd check with fellow math-funsters rather than risk embarrassing myself with an incorrect letter to the editors.
Andy Latto andy.latto@pobox.com
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