Question

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
She will not buy it ?

Answer 1

Sample space $=144$ ball pens
Good pens $144-20=124$
Defective Pens $=20$
Probability that she will buy $=\frac{goodpens}{SampleSpace}$ $=\frac{124}{144}$
Probability that she will not buy $=\frac{defectivepens}{SampleSpace}$ $=\frac{20}{144}=\frac{5}{36}$