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, 

Answer 1

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`