Short Note

Sum

A lot consists of 144 ballpoint pens of which 20 are defective and others good. Tanvy will buy a pen if it is good, but will not buy it if it is defective. The shopkeeper draws one pen at random and gives it to her. What is the probability that she will not buy it?

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#### Solution

Let E_{2} be the event of getting a defective pen.

∴ P(not buying a pen) = P(E_{2}) = `("Number of outcome favourable to" E_2)/"Number of all possible outcomes"`

`=20/144 = 5/36`

Thus, the probability that Tanvy will not buy a pen is `5/36`

Concept: Basic Ideas of Probability

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