Question

A shelf in the Metro Department Store contains 90 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

A ) 
P ( x = 3 ) = 5/90 * 4/89 * 3/88  = 1 / 11,748 = 0.000085
b ) 
Probability of selecting zero defective cartridges:
P ( x = 0 ) = 85/90 * 84/89 * 83/88 = 592,620 / 704,880 = 0.840739
P ( at least 1 defective) = 1  -  0.840739 = 0.159261