Question

Defective pens are accidentally mixed with 132 good ones. It is not possible to just look at pen and tell whether or not it is defective. 1 pen is taken out at random from this lot. Find the probability that the pen taken out is 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.

Therefore, P(getting a good pen) = P(E) = \(\frac{number\,of\,outcomes\,favorable\,to\,E}{number\,of\,all\,possible\,outcomes}\) = \(\frac{132}{144}\) = \(\frac{11}{12}\)

Thus, the probability of getting a good pen is \(\frac{11}{12}\).