Question

$12$ defective pens are accidentally mixed with $132$ good pens. 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 good one.

• A. $\frac{11}{12}$
• B. $\frac{11}{14}$
• C. $\frac{13}{14}$
• D. $\frac{11}{15}$

Answer 1

The correct option is A $\left(\frac{11}{12}\right)$

Number of good pens $=132$
Number of defective pens $=12$
$\therefore$ Total pens $=132+12=144$
Probability of an event $\left(A\right)$ is $=\frac{n\left(A\right)}{n\left(S\right)}$
Where $n\left(A\right)$ is the number of favourable outcomes.
$n\left(S\right)$ is the total number of outcomes.
Probability of getting good pens = $\frac{132}{144}=\frac{11}{12}$