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Question
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 buy it,
Solution
Total number of pens = 144
Number of defective pens = 20
Number of good pens = 144 − 20 = 124
Let E1 be the event of getting a good pen.
∴ P(buying a pen) = P(E1) = `("Number of outcomes favourable to" E_4)/ "Number of all possible outcome" `
`124/144 = 31/36`
Thus, the probability that Tanvy will buy a pen is `31/36`
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