A and B are events such that P(A) = 0.4, P(B) = 0.3 and P(A B) = 0.5. Then P (B′ A) equals


We have,

P(A) = 0.4, P(B) = 0.3 and P(A B) = 0.5


Now,


P(A B) = P(A) + P(B) – P(A B)


[Additive Law of Probability]


0.5 = 0.4 + 0.3 – P(A B)


P(A B) = 0.7 – 0.5


P(A B) = 0.2


P(B’ A) = P(B’) P(A)


= [1 – P(B)]× P(A)


[sum of the probabilities of an event and its complement is 1]


= P(A) – P(A)P(B)


= P(A) – P(A B)


= 0.4 – 0.2


= 0.2



Hence, the correct option is D

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