Suppose you pick and replace marbles from a bag, one after another. If the bag contains 3 red marbles, 3 white marbles, and 6 blue marbles, what is the probability of picking a red marble and then a blue marble?
There are 3 + 3 + 6 = 12 marbles in the bag and 12 * 12 = 144 ways to choose two marbles when replacing. There are 3 * 6 = 18 ways to choose a red marble and then a blue marble so the probability is 18 / 144 = 1 / 8.
