You're in a room lled with two types of urns: Type X urns contain 2 black marbles and 3 white marbles, and Type Y urns contain 4 black marbles and 1 white marble. The two types of urns look identical, but 60% of them are Type Y. You pick an urn at random and draw two marbles at random without replacement. The rst is black and the second is white. What is the probability that on a third draw you'll draw a black marble