Given a standard 52 card deck, what is the expected number of cards needed to draw until we have two cards with the same number?
It's not hard to do for a fixed value (say fix Kings, then deck order can be _K__K__K__K__, all other cards have 1/5 probability of being in each space, so we expect 48*2/5 + 2 = 21.2 cards to be drawn before we find 2 Kings). Is the solution similar when the value is not fixed?