Question 21 (i)
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 she will buy it?

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Solution

Total number of outcomes = 144
Number of non - defective pens = 144 - 20 = 124
$∴$ Number of favourable outcomes = 124
Hence, P (Nuri buys a pen) = P (choosing a non - defective pen)
$= \frac{124}{144} = \frac{31}{36}$

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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?

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Theoretical Probability

Standard IX Mathematics

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Question 21 (i) 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 she will buy it?

Total number of outcomes = 144 Number of non - defective pens = 144 - 20 = 124 ∴ Number of favourable outcomes = 124 Hence, P (Nuri buys a pen) = P (choosing a non - defective pen) =124144=3136

Question 21 (i)
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 she will buy it?

Total number of outcomes = 144
Number of non - defective pens = 144 - 20 = 124
$∴$ Number of favourable outcomes = 124
Hence, P (Nuri buys a pen) = P (choosing a non - defective pen)
$= \frac{124}{144} = \frac{31}{36}$