Question

A shipment contains 10 good and 4 defective bulbs. If three bulbs are selected without replacement, determine the probability the third is defective given the first two are good.

Answer 1

1/3

Explanation:

Since you know the first two are good, they do not factor in. The only difference now is your total.

You had a total of 14 bulbs, but two were removed and we know they're good.

Now you have a total of 12 bulbs. 4 are still defective. Your probability of pulling a defective one is 4/12, or reduced, 1/3.