From 'Elementary Statistics A step by Step approach:

A box contains 24 transistors, four of which are defective. If four are

sold at random, find the following probabilities:

a) Exactly two are defective

b) None is defective

c) All are defective

d) At least one is defective

Why can't you use the multiplication rule for part A? it works for all of the other examples. I understand the steps to solve, I just don't understand why you can not solve using multiplication rule.

(4/24)(3/23)(20/22)(19/21)... this gives you about 1.8%. if you solve using combinations it gives you 10.8%.