Question

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

Answer 1

Given that $:$

$12$ defective pens are accidentally mixed with $132$ good ones$.$ One pen is taken out at random.

Find out the probability that the pen is taken out is a good one$.$

Numbers of pens $=$ Numbers of defective pens $+$ Numbers of good pens

∴ Total number of pens $=132+12$

$=144$ pens

Let $E$ be the event of getting a good pen$.$

$P\left(E\right)=$$($Number of favourable outcomes$/$Total number of outcomes$)$

$P\left(E\right)=$$\frac{132}{144}$

$=\frac{11}{12}$

$=0.916$

Hence$,$ the probability that the pen is taken out is a good one is $0.916$