4 Suppose that is known that a parent has two children, but the genders of the children are not known. You go to the house where they live to find out. (a) Suppose that when you knock on the door, the parent answers. You start by asking them if at least one of their children is a girl and they answer "yes." What is the probability that both of the children are girls? (b) Suppose instead that when you knock on the door, one of the children answers and you see that she is a girl. What is the probability that both of the children are girls? Why is this not the same answer as before?