21.(ii)   A lot consists of 144 ball pens of which 20 are defective and the others are good. Nuri will buy a pen if it is good, but will not buy if it is defective. The shopkeeper draws one pen at random and gives it to her. What is the probability that (ii) She will not buy it ?

Answers (1)

Total number of pens = 144

Total number of defective pens = 20

She will buy if the pen is good.

Therefore, probability that she will not buy = probability that the pen is defective = 

P(getting\ a\ defective\ pen) = \frac{no.\ of\ defective\ pens}{total\ pens}= \frac{20}{144}

= \frac{5}{36}