If A and B are events such that P(A) =p1 , P(B)= p2  and P(A∩B)=p3  then P(A¯∪B)=

P(A¯∪B)=P(A¯)+P(B)−P(A¯∩B)                     =1−P(A)+P(B)−{P(B)−P(A∩B)}                     =1−P(A)+P(A∩B)                     =1−p1+p3