Given P(A) = 0.6, P(B) = 0.5 and P(A and B) = 0.2, the value of P(A given B) is:

解說

P(A given B) = P(A and B) / P(B) = 0.2 / 0.5 = 0.4. Note that this is smaller than P(A) = 0.6, because knowing B occurred makes A less likely.