Question

A lot consists of $144$ ball pens of which $20$ are defective and the other are good. Nuri 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. What is the probability that

(i) she will buy it?

(ii) she will not buy it?

Answer 1

Total number of pens $=144$

Number of defective pens $=20$

Number of good pens $=144–20=124$

(i) Probability that she will buy it $=\frac{numberofpossibleoutcomes}{totalnumberoffavourableoutcomes}$

$=\frac{124}{144}$

$=\frac{31}{36}$

(ii) Probability that she will not buy it $=\frac{numberofpossibleoutcomes}{totalnumberoffavourableoutcomes}$

$=\frac{20}{144}$

$=\frac{5}{36}$

Hence (i) Probability that she will buy it $=\frac{31}{36}$ and (ii) Probability that she will not buy it $=\frac{5}{36}$