Tom, a holiday light inspector, has to check a shipment of multicolored Christmas lights. Suppose that the probability of a defective lightbulb is 30%.

Question

a. Find the expected number of bulbs that Tom has to go through until he finds one that is defective.

b. Find the probability that the first defective bulb that Tom finds is the 8^th bulb.

c. Find the probability that Tom finds 3 defective light bulbs among 12 bulbs.

Answer 1

a) I am not sure but the answer should be Infinite

b) P₈= (0.7)⁷(0.3)

c) Probability = 12C3 * (0.3)³