Question

Probability of occurrence of event a is 0.5 and that of event b is 0.2. the probability of occurrence of both a and b is 0.1. what is the probability that none of a and b occur?

Answer 1

probability of sure event = 1
probability of occurrence of event a= 0.5
Probability of occurrence of event b =0.2
probability of occurrence of both a and b = 0.1
probability of none =1-0.8=0.2

Answer 2

P(A∪B)=P(A)+P(B)−P(A∩B)  

⇒0.2 + 0.5 - 0.1

⇒0.6

P(A∪B)′ = 1−P(A∪B)

⇒1−0.6

⇒0.4