In a box of 12 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?
I have another way to solve by using combinations.
First, there are 9C2 ways you can select 2 good pencils from 9 good ones.
Second, there are 12C2 ways you select 2 pencils from 12 ones in the box.
Then, the probability that neither pen will be defective is: 9C2/12C2=6/11
Song of the day: To be with you- David Archuleta