Question

assume one family has two children, one of them is a boy. what is the probability that the other is also a boy?

Answer 1

1/3

Explanation:

This answer is unintuitive, but stick with me.

If a family has 2 children, and each can be a boy (B) or a girl (G), there are 4 possible combinations:

BB BG GB GG

We know that this family doesn't have 2 girls, leaving us with 3 options:

BB BG GB

Because the order is unspecified, all 3 of these options are possible. Only one has two biys out of 3 possibilities, so it is 1/3.