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

Answer 1

(i) Here, total number of bulbs `= 20`
Number of defective bulbs `=4`
So, probability of drawing a defective bulb `= 4/20 = 1/5`

(ii)If drawn bulb is not defective and not replaced, then
Remaining number of total bulbs `= 19`
Remaining number of defective bulbs `=4`
So,remaining number of non-defective bulbs `=15`
Probability of drawing a non-defective bulbs `= 15/19`