Question

A lot consists of 144 ball pens of which 20 are defective and the others are good. Tanu will buy a pen if it is good but will not buy it if it is defective. The shopkeeper draws one pen at random and gives it to her. The probability that she will buy that pen is ____________.

Options

• `5/36`

• `20/36`

• `31/36`

• `31/144`

Answer 1

A lot consists of 144 ball pens of which 20 are defective and the others are good. Tanu will buy a pen if it is good but will not buy it if it is defective. The shopkeeper draws one pen at random and gives it to her. The probability that she will buy that pen is `underline(31/36)`.

Explanation:

Total ball pens = 144

Defective ball pens = 20

Good ball pens = 144 - 20 = 124

`therefore "P(she will buy a pen) = P(good ball pen)" = 124/144 = 31/36`