A drawer contains 3 white balls and 6 black balls. Two balls are drawn out of the box at random. What is the probability that they both are black?
there are 9 balls total in the drawer
the probability that the first one is black is 6/9=2/3
the probability that the second is black (with the first one drawn being black also) is (6-1)/(9-1)=5/8
multiply the probabilities: