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

Answer 1

Correct Answer - ` (i) 1/5 (ii) 15/19`
(i) Total number of bulbs = 20. Number of defective bulb = 4.
Number of non-defective bulbs = 20- 4= 16.
`:. ` P(getting a defective bulb) = ` 4/20 = 1/5`.
(ii) After removing 1 non-defective bulb, we have remaining number of bulbs = 20-1 = 19.
Out of these, the number of non-defective bulb = 16-1=15.
` :. ` P(getting a non=defective bulb) = ` 15/19`.