$A$ lot consists of $144$ ball pens of which $20$ are defective and the others are good. Nuri will buy a pen if it is good,but will not buy if it is defective. The shopkeeper draws one pen at random and gives it to her. What is the probability that
$(i)$ She will buy it?
$(ii)$ She will not buy it?

(A) Total number of pens $= 144$
Total number of defective pens $= 20$
Total number of good pens $= 144 - 20 = 124$
$(i)$ Probability of getting a good pen (Nuri buys the pen) $= \frac{124}{144} = \frac{31}{36}$
$(ii)$ Probability of getting a defective pen (Nuri will not buy the pen) $= \frac{20}{144} = \frac{5}{36}$ or $1 - \frac{31}{36} = \frac{5}{36}$