If we take a sample of 2400 families with five children,
a) what is the probability that a family will have exactly 2 girls?
b) How many of the families would you expect to have exactly two girls?
Binomial distribution gives us
5C2*(.5)²(.5)³
=10(.5)^5
=0.3125
E(x)=2400*0.3125=750