Question

12 defective pens are accidentally mixed up with 132 good ones. It is not possible to just look at a pen and tell whether it is defective or not. One pen is taken out at random from the lot. Find the probability that the pen taken out is a good one.

Answer 1

Total number of pens = 132 + 12 = 144

Number of good pens = 132

Let E be the event of getting a good pen.

∴ P(getting a good pen) = P(E) = `"Number of outcome favourable to E"/"Number of all possible outcomes"`

`=132/144 = 11/12`

Thus, the probability of getting a good pen is `11/12`.