A couple want to have one girl and one boy. What is the expected number of children they will have?
I know that the answer is 3 and that the question relates to the Negative Binomial distribution but I'm not sure how to solve this. Can anyone explain?
Maybe negative binomial is overkill here. It’s a geometric+1.
First they will have a child. And then they will keep having more children until they have one of the opposite sex.
So the expectation will be 1 plus the expectation of a geometric, which is 2. So in total 3