college
posted by Jess on .
Given 24 pens, either red or blue. If 4 are blue, what is the probability of you select 2 pens AT LEAST 1 will be blue. (without replacement, that is, you are taking 2 separate pens)

Add the probabilities of:
bluered, redblue and blueblue.
(4/24)*(19/23) + (20/24)*(4/23) + (4/24)(3/23) = [76 + 76 + 12)/552 = 164/552
= 41/138