Shipment 20 computers are ramdomly selected and tested probability that all three are defective if the first and second are no replaced and if are replaced

Question

probability

Answer 1

Assume the problem is this:

In a shipment of 20 computers 5 are defective. Three are randomly selected and tested. What is the probability that all three are defective,

a) if the first and second are not replaced, and

b) if they are replaced.

 

a) 5/20 * 4/19 * 3/18 = 1/4 * 4/19 * 1/6 = 1/(19*6) = 1/114

 

b) 5/20 * 5/20 * 5/20 = 1/4 * 1/4 * 1/4 =1/64