A woman has two kids. One is a boy. What are the odds the other is a boy?

Or so you think.

Consider the four possibilities for having two children:

B/B
B/G
G/B
G/G

We can eliminate G/G because we know that one of them is a boy. This leaves B/B, B/G and G/B. Only 1 in 3 has the other as a boy also.

This only matters if the order in which they are born makes a difference, which it doesn't in this case. So I'm sticking with 50%