# 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 ?

**Solution:**

We use the basic formula of probability and favourable outcomes.

Total number of ball pens = 144

Number of defective ball pens = 20

Number of good ball pens = 144 - 20 = 124

(i) Probability that she will buy it = Number of possible outcomes/Total number of favourable outcomes

= 124/144

= 31/36

(ii) Probability that she will not buy it = Number of possible outcomes/Total number of favourable outcomes

= 20/144

= 5/36

Check out more information about terms of probability.

**Video Solution:**

## 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 ?

### NCERT Solutions for Class 10 Maths Chapter 15 Exercise 15.1 Question 21 - Chapter 15 Exercise 15.1 Question 21:

**Summary:**

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. If the shopkeeper draws one pen at random and gives it to her. The probability that (i) She will buy it is 31/36 and (ii) She will not buy it is 5/36.