已知P(A拔)=0.3,P(B)=0.4,P(AB拔)=0.5,求条件概率P(B|A+B拔).

P(B)=0.4,可得P(B拔)=0.6
P(AB拔)=0.5
P(A拔)=0.3,可得P(A)=0.7
P(A+B拔)=P(A)+P(B拔)-P(AB拔)=0.7+0.6-0.5=0.8
P(B(A+B拔))=P(AB)=P(A)-P(AB拔)=0.7-0.5=0.2
P(B|A+B拔)=P(B(A+B拔))/P(A+B拔)=1/4