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

(i) She will buy it?

(ii) She will not buy it?

Answer 1

Total number of pens $=144$

Total number of defective pens $=20$

Total number of good pens $=144-20=124$

Probability an outcome $=\frac{\text{number of favourable outcome}}{\text{total number of possible outcomes}}$

(i) Probability of getting a good pen $=\frac{124}{144}=\frac{31}{36}$

P (Nuri buys a pen) $=\frac{31}{36}$

(ii) P (Nuri will not buy a pen) $=1-\frac{31}{36}$
$=\frac{36-31}{36}$
$=\frac{5}{6}$