Question

12 defective pens are mixed with 120 good ones.
One pen is taken out at random from this lot.
Determine the probability that the pen taken out is not defective.

Answer 1

$$\begin{gathered} \mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{pens}=120+12=132 \\ \mathrm{Probability}\left(\mathrm{pen}\mathrm{is}\mathrm{not}\mathrm{defective}\right)=\frac{\mathrm{Number}\mathrm{of}\mathrm{good}\mathrm{pens}.}{\mathrm{Total}\mathrm{number}\mathrm{of}\mathrm{pens}}=\frac{120}{132}=\frac{10}{11}\mathrm{ANS}... \end{gathered}$$