In a box having 4 bulbs, the probability of having one defected bulb is 0.5 and the probability of having no bulb defected is 0.4, Find the probability of having one defected bulb or zero defected buib. Solution: Probability of 1 bulb being defected, P(A)=0.5P(A)=O.5 Probability of O bulb being defected, P(B)=0.4P(B)=O.4 As there can be either 1 defected bulb or zero defected bulb as these two events cannot happen together, they are mutually exclusive. Probability of having one bulb or zero bulb defected, P(A or B)=0.5+0.4=0.9