Question

In a shipment of 20 computers, 3 are defective. two computers are randomly selected and tested. what is the probability that both are defective if the first is not replaced after being tested?

Answer 1

You have to use the multiplication rule.
The probability that the fisrt one is defective: 3/20
And the probability that the second one is also defective and you can not replace the first computer drawn is: 3/20*2/19 = 3/190 = 0.0158