Suppose that a family has
3
children. Also, suppose that the probability of having a girl is
one half 1/2.
Find the probability that the family has the following children.
Exactly
2
girls
and
1
boy
deleted.... see below
You need to consider the order in which they could be born, so the possibilities are:
1st born. 2nd born. 3rd born.
B. B. B
B. B. G
B. G. B
G. B. B
B. G. G
G. B. G
G. G. B
G. G. G
So the probability of exactly 2 girls and 1 boy is 3/8.
P(2 girls) = C(3,2) (1/2)^3 = 3 * (1/8) = 3/8
+20 
