Question

A box contains 15 pens of which 4 are defective. A random sample of 3 pens is taken without replacement and without regard to order. What is the probability of selecting at least one defective pen?

Answer 1

What you want in the probability of selecting 1, 2 or 3 defective pens.

P of 3 = 4/15 * 3/14 * 2/13

P of 2 = 4/15 * 3/14 * 11/13

P of 1 = 4/15 * 11/14 * 10/13

The answer is the sum of those three products.

Answer 2

0.2442