Thanks, Franklin: << Oh, yes, the following should be easy assuming a society where boys and girls are born in roughly even numbers. If you know a family has two kids and you see one playing outside and the kid is a girl, what is the chance that the other is a girl?

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Interesting that even if a parent informs you that they have two children, and flips a coin to decide which child's sex to divulge to you (and it's a girl), the probability is still 1/2 that the other child is a girl. --Dan