There are 5 red and 4 black balls in a box. If three balls are picked without replacement, what is the probability that at least one of them is red?

Answer 1

First, let's consider the probability that none of the balls are red, or all of them are blue. There are 9 balls, 4 of which are blue. So the chance that 3 blue balls will be chosen is 4/9 * 3/8 * 2/7, or 1/21. You can do the rest from here.