0 like 0 dislike
43 views
Your new neighbors have 2 children and you know at least one of them is a boy. You see one of them playing in the backyard and he is a boy - what is the probability the other child is a boy too? (Assume boys and girls are born with equal probability)
| 43 views

0 like 0 dislike
It's important to realize that you don't know whether you are looking at the younger or older child. The children could have been born in the following ways: $B B, B G, G B$. We are excluding the possibility that the children were born $G G$, since we know that one of the kids is a boy.
$P(2$ boys $\mid$ at least 1 boy $)=P(B B) / P(B B \cup B G \cup G B)=1 / 3$
by Diamond (40,719 points)

1 like 0 dislike
0 like 0 dislike
0 like 0 dislike
0 like 0 dislike
0 like 0 dislike
0 like 0 dislike
1 like 0 dislike
0 like 0 dislike
1 like 0 dislike