No. of good pens = 144 – 20 = 24

No. of detective pens = 20

Total no. of possible outcomes = 144 {total no pens}

**(i) E ⟶ event of buying pen which is good.**

No. of favourable outcomes = 124 {124 good pens}

P(E) = (No.of favorable outcomes)/(Total no.of possible outcomes)

P(E) = 124/144 = 31/36

**(ii) Bar E⟶ event of not buying a pen which is bad P(E) + P(Bar E) = 1**

P(E)+P(Bar E)=1

P(Bar E) = 1 - P(E)

=1−31/36 = 5/36