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# 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?

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

(i) she will buy it.

(ii) She will not buy it.

Solution:

Total number of ball pens $=144$

This implies,

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

(i) 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 $\frac{31}{36}$.

(ii) Number of defective pens $=20$

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

Total number of favourable outcomes(she will not buy it) $=20$.

We know that,

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

Therefore,

Probability that she will not buy the pen $=\frac{20}{144}$

$=\frac{5}{36}$

The probability that she will not buy it is $\frac{5}{36}$.