In a two child family, one of the children is a boy - not known whether older or younger. What is the probability that both children are boys? The answer is not 50%. What is it and why?
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one child is a boy. you dont know the age... could be unborn. which adds another possibility.
the total possibilities are
2 boys
1 boy, 1 girl
1 girl, 1 boy
chance is 1/3
not 1/2
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