If there is an equal probability of a child being born a boy or a girl, what is the probability that a couple who have 7 children have two children of the same sex and one of the opposite sex?
Choices
A) 1/3  B) 2/3  C) 1/4  D) 7/64  E) 3/5
No of ways of selecting a gender - 2C1   No of ways of selecting any 2 children out of 7 = 7C2   Total possible outcomes - 2^7 (each child can be either a girl or a boy)   Probability=2C1*7C2/2^7= 2*7/2*2*2*2*2*2*2=7/64   Ans=7/64
<result>D</result>
If there is an equal probability of a child being born a boy or a girl, what is the probability that a couple who have 7 children have two children of the same sex and one of the opposite sex?