A retailer of personal computers just received a shipment of

A retailer of personal computers just received a shipment of 30 units of a new model. The store has a quality agreement with the manufacturer which states that four of the machines are to be selected for a thorough performance check. If more than one fails a performance test the shipment is returned. Suppose the retailer did not know that 5 of the 30 incoming computers are defective. Compute the probability exactly two computers selected at random are defective.

Solution

P = 5/30 = 0.17

Q = 1- 0.17 = 0.83

n = 4

P( x=2 ) = 4C2 * 0.17^2 * 0.83^(4-2) = 0.1195