Afamily decides to have children until it has three children of the same gender. assuming p(b)=p(g)=.5,. what is the pmf of x = the number of children in the family? . this problem was in the section of negative binomial distribution in the textbook and i used the equation for nb but the sum of all the probabilities is just 0.5. and, i saw in yahoo someone using the p(a)= n(a)/n and getting the sum of p(x)=1. also, it made sense for this problem as both the events were equally likely-- p(b)=p(g)=0.5. but, shouldn't nb also give the same result as of using the classical definition?