(i) A lot of 20 bulbs contain 4 defective ones.

GIVEN: A lot of 20 bulbs contain 4 defective ones. One bulb is drawn at random from the lot

TO FIND: Probability that it is defective

Total number of bulbs is 20

(i) Total numbers of bulbs which are defective is 4

We know that PROBABILITY = 

Hence probabilities of bulbs which are defective is 

(ii) Suppose the bulb drawn in case (i) is not defective and not replaced

Then total number of bulbs will be 19.

Total numbers of bulbs which are not defective is 

We know that PROBABILITY = 

Hence probabilities of bulbs which are not defective are