Last week, Slashdot posted an interesting link to a problem posed at the most recent Gathering 4 Gardner, a mathematical (or perhaps I should say mathemagical) convention created in honor of the late Martin Gardner. The question, posed by Gary Foshee, is as follows: you have a friend with two children, one of whom is a boy born on a Tuesday. What is the probability that the other child is a boy?

Forget about the Tuesday fact for a moment – if you have a friend with two children, one of whom is a boy, what is the probability that the other child is a boy? You might expect that the answer should be 50%, since the sex of one child shouldn’t affect the sex of the other. But this is not quite right, because you’re not told whether the boy is the older or younger child.

There are only . . . → Read More: A New Birthday Problem