You have fifteen marbles in five colors:  one white marble, two red marbles, three yellow marbles, four blue marbles, and five green marbles.  Find a way to distribute the marbles between two urns so that, when two marbles are drawn randomly from the first urn and two from the second urn, the probability that the four marbles drawn will have four different colors is exactly one in three (1/3).  Solution

Questions, corrections, comments:  Send me e-mail at  markthom@flash.net