RD Sharma Solutions Class 10 Mathematics Solutions for Probability Exercise 13.1 in Chapter 13 - Probability

Question 92 Probability Exercise 13.1

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.



When an experiment is repeated numerous times under identical circumstances, the proportion (or relative frequency) of times that the event is anticipated to occur is known as the probability of the event.

No. of good pens = 144 – 20 = 124

No. of detective pens = 20

Total no. of possible outcomes =144 (total no. of pens)

For her to buy it the pen should be a good one.

So, let E = event of buying a pen which is good.

No. of favourable outcomes = 124 (124 good pens)

Probability, P(E) = Number of favourable outcomes/ Total number of outcomes

P(E) = 124/144 = 31/36

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