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May 13, 2013 at 17:22 comment added user112109 @Timothy: E[G/(B+G)] is not interesting in order to find "the fraction of female population". For that sake we need E[G]/E(B] and that is 1 because the sex of a child does not depend on the history of the mother.
Jul 9, 2010 at 0:31 comment added T.. Timothy, it only matters what quantity you ask for if you change the problem from the original to the one solved in Zare's much-upvoted answer. See my reply to his posting.
Jul 8, 2010 at 19:06 comment added Timothy Chow Daniel, I think you still don't understand Zare's insight. It matters exactly what quantity you're asking for. If G is the number of girls and B is the number of boys then "the proportion of girls in the population" is naturally interpreted as G/(B+G). The fact that E[G] = E[B] doesn't imply that E[G/(B+G)] = 1/2.
Jul 6, 2010 at 23:12 comment added Daniel Asimov Zare falls into exactly the trap I mention in my first paragraph.
Jul 6, 2010 at 1:31 comment added Timothy Chow Daniel, it looks like you haven't studied Douglas Zare's answer very carefully. He has made a very striking new observation about this old chestnut.
Jul 5, 2010 at 21:27 history edited Daniel Asimov CC BY-SA 2.5
added comment about Google's phrasing of the problem
Jul 5, 2010 at 21:16 history edited Daniel Asimov CC BY-SA 2.5
corrected grammar
Jul 5, 2010 at 21:11 history answered Daniel Asimov CC BY-SA 2.5