Question

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 she will buy it?

Answer 1

Total number of outcomes = 144
Number of non - defective pens = 144 - 20 = 124
$\therefore$ Number of favourable outcomes = 124
Hence, P (Nuri buys a pen) = P (choosing a non - defective pen)
$=\frac{124}{144}=\frac{31}{36}$