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Monday, June 29, 2015

A Re-run Monday


I was reading the first of Greg Ross's "Futility Closet" volumes when I came across one of my favorite old puzzles, that was last presented here over 2 years ago. I originally learned of it from Richard Wiseman's blog and again I'll opt for Richard's version of it (most readers here are likely already familiar with it):
"Imagine there is a country with a lot of people. These people do not die, the people consist of monogamous families only, and there is no limit to the maximum amount of children each family can have. With every birth there is a 50% chance it's a boy and a 50% chance it is a girl.  Every family wants to have one son: they get children until they give birth to a son, then they stop having children. This means that every family eventually has one father, one mother, one son and a variable number of daughters.  What percent of the children in that country are male?"
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(p.s.  also, be sure to check out MathTango today for my interview with Siobhan Roberts, author of the brand-spanking new "Genius At Play" biography of John Conway.)
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The answer (surprising to some, not to others) is 50%, which I won't explain, but will direct you to Richard's post (and 270+ comments) if you need an explanation:
http://richardwiseman.wordpress.com/2012/01/16/answer-to-the-friday-puzzle-139/


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