Assuming a 11 sex ratio what is the probability that 5 child

Assuming a 1:1 sex ratio, what is the probability that 5 children produced by the same parents will consist of a daughter as the oldest and a son as the youngest?

Solution

Answer:

Probability of first child being a girl (eldest daughter) = ½

Probability of last child being a youngest son is = ½

(probability of getting eldest daughter) x (probability of getting youngest son) = (1/2) x (1/2) = 1/4