# 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.

**☛ Check: **NCERT Solutions for Class 10 Maths Chapter 15

**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

**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.

**☛ Related Questions:**

- (i) Complete the following table:(ii) A student argues that ‘there are 11 possible outcomes 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12. Therefore, each of them has a probability 1/11. Do you agree with this argument? Justify your answer.
- A game consists of tossing a one-rupee coin 3 times and noting its outcome each time. Hanif wins if all the tosses give the same result i.e., three heads or three tails, and loses otherwise. Calculate the probability that Hanif will lose the game.
- A die is thrown twice. What is the probability that(i) 5 will not come up either time?(ii) 5 will come up at least once?[Hint : Throwing a die twice and throwing two dice simultaneously are treated as the same experiment]
- Which of the following arguments are correct and which are not correct? Give reasons for your answer. (i) If two coins are tossed simultaneously there are three possible outcomes—two heads, two tails or one of each. Therefore, for each of these outcomes, the probability is 1/3⋅ (ii) If a die is thrown, there are two possible outcomes—an odd number or an even number. Therefore, the probability of getting an odd number is 1/2.

visual curriculum