Question

A shelf in the Metro Department Store contains 95 colored ink cartridges for a popular ink-jet printer. Five of the cartridges are defective.
(a) If a customer selects 3 cartridges at random from the shelf, what is the probability that they are all defective? (Round your answer to five decimal places.)

(b) If a customer selects 3 cartridges at random from the shelf, what is the probability that at least 1 is defective? (Round your answer to three decimal places.)

Answer 1

(7C3 * 73C0) / 80C3
 but that = (35 * 1) / 80C3
= 35 / 82160
 = .00043 

For B

(7C1 * 73C2 + 7C2 * 73C1 + 7C3 * 73C0) / 80C3
 = 19964 / 82160 = .243
hope it helps