Discrete Math
posted by Steven .
A bag contains 5 red marbles, 4 yellow marbles, 3 green marbles, 2 orange marbles and 2 purple marbles. If three marbles are removed, what is the probability that at least one of them is red?

Since there are 5 red marbles and 11 others, then the chance is
11/16 * 10/15 * 9/14 = 33/112 that the first three draws are not red.
So, that leaves 79/112 chance that at least one was red.