Finite math
posted by MV .
A newly married couple decides to keep having children until they have a girl. What is the probability that the couple will have at least 5 children?

This is Geometric distribution.
Let Y be r.v."No: of chldn before a girl"
P(Y=y)=pq^(y1)...therefore
P(Y=5)=(0.5)(0.5)^(51)=0.03125.