A lot of 20 bulbs contain 4 defective ones. One bulb is selected at random from the lot. What is the probability that this bulb is defective? Suppose the bulb selected in previous case is not defective and is not replaced. Now one bulb is selected at random from the rest. What is the probability that this bulb is not defective?

Five cards- the ten jack. Queen. King and ace of diamonds. Are well- shuffled with their face downwards. One card is selected at random.

If the queen is selected and put aside (without replacement). What is the probability that the second card selected is (a) an ace ? (b) a queen ?

12 defective pens are accidentally mixed with 132 good ones. It is not possible to just look at a pen and tell whether or not is defective. One pen is taken out at random from this lot. Determine the probability that the pen taken out is a good one.

A box contains 90 discs which are numbered from 1 to 90. If one disc is selected at random from the box, find the probability that it bears.

a two- digit number

A box contains 90 discs which are numbered from 1 to 90. If one disc is selected at random from the box, find the probability that it bears.

a perfect square number