A shipment of 24 electric typewriters is rejected if 3 are checked for defects and at least 1 is found to be defective Find the probability that the shipment will be returned if there are actually 6?

Answer 1

You keep them if you test 3 and all pass.

There are 18 good ones and 6 bad (making 24)

Chance of first passing is 18/24

If it passes, there are now one less good and one less total.

Chance of second passing is 17/23

If it passes, there are now one less good and one less total.

Chance of second passing is 16/22

Total is (16 x 17 x 18) / (22 x 23 x 24) = about 0.4 (0.403162055 is you really want to know).

So probability all are ok is 0.4

Thus probability you find at least one bad one is 0.6

Answer 2

1.3