Andy Latto 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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I completely concur with you, but that this is notoriously tricky AND that the article got it wrong. The probability you seek is NOT: P{both are girls | at least one is a girl} but rather P{both are girls | the one outside is a girl} In the author's examples, it's like the penny and dime where the dime is known. David