1. The problem statement, all variables and given/known data An urn contains 4 white and 4 black balls. We randomly choose 4 balls. IF 2 of them are white and 2 are black, we stop. If not, we replace the balls in the urn and again randomly select 4 balls. this continues until exactly 2 of the 4 chosen are white. What is the probability that we shall make exactly n selections. 2. Relevant equations 3. The attempt at a solution I don't see why I can't find the probability of drawing exactly 2 white balls using this method. (4C2)(4/8)^2(1-4/8)^2 where 4C2 is 4 choose 2 apparently this is wrong but I don't see why. Thanks for any help that you can provide.