There is a bag in front of me. I am told it contains 100 red balls or 50 red balls and 50 blue balls. If I pick n red balls from the bag and no blue balls what is the probability as a function of n (p(n)) that the bag contains 50 red balls and 50 blue balls. Of course, if n is greater than 50 then p(n)=0, but what about for n less than or equal to 50?!