We have,
No. of good pens $=132$
No. of defective pens $=12$
Therefore, the total no. of pens $=132+12=144$
Then we have, the total no. of possible outcomes $=144$
Now, let E be the event of getting a good pen.
So No. of favorable out comes $=132$ ($132$ good pens)
As we know the Probability, P(E) = Number of favorable outcomes/ Total number of outcomes
P(E) $=132/144=11/12$