Question

15 defective ballpens are accidentally mixed with 135 good ones. It is not possible to just look
at a ballpen and say whether it is defective or not. One ballpen is picked up a random from it.
Find the probability that the ballpen selected is a good one,​

Answer 1

Answer:

Good Pens + Defective Pens

$= 135 + 15 = 150$

$n \: (s) \: = 150$

$= > \: p \: (a) \: = \frac{n(a)}{n(s)} = \frac{135}{150} = \frac{9}{10}$