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# A lot consists of 144 ball pens of which 20 are defective and others 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?

Given:

A lot consists of 144 ball pens of which 20 are defective and others 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.

To do:

We have to find the probability that she will buy it.

Solution:

Total number of ball pens $=144$

This implies,

The total number of possible outcomes $n=144$.

Number of defective pens $=20$

Number of good pens $=144-20=124$

Total number of favourable outcomes(she will buy it) $=124$.

We know that,

Probability of an event $=\frac{Number\ of\ favourable\ outcomes}{Total\ number\ of\ possible\ outcomes}$

Therefore,

Probability that she will buy the pen $=\frac{124}{144}$

$=\frac{31}{36}$

The probability that she will buy it is $\frac{31}{36}$.