Question

(i) A lot of 20 bulbs contain 4 defective ones. One bulb is drawn at random from the lot. What is the probability that this bulb is defective?

(ii) Suppose the bulb drawn in

(a) is not defective and nõt replaced. Now bulb is drawn at random from the rest. What is the probability that this bulb is not defective?

Answer 1

Total no. of possible outcomes = 20 {20 bulbs}

(i) E ⟶ be event of getting defective bulb.

No. of favourable outcomes = 4 {4 defective bulbs}

Probability, P(E) = (No.of favorable outcomes)/(Total no.of possible outcomes) = 4/20 = 1/5

(ii) Bulb drawn in is not detective & is not replaced remaining bulbs = 15 good + 4 bad bulbs = 19

Total no. of possible outcomes = 19

E ⟶ be event of getting defective

No. of favorable outcomes = 15 (15 good bulbs)

P(E) = 15/19