A couple decide that they will keep having children until they have one of each sex. (stop as soon as they have both girl and boy or at 4 children regardless of sex). Ignoring the possibility of twins and suppose each trial is independent, and resuts in a boy or girl with probability 1//2. Let X be the number of children they will have.
a) What is the pmf of X?
b) What is the expected number of X or what is the mean?
Both need to be answered