中考真题概率分析

P(A∩B)/P(B)=1/4

P(A∩B) =1/8

P(~A|~B)

=P(~A∩~B) /P(~B)

=P(~(AUB) ) /[1 -P(B)]

=[1-P(AUB)]/[1-P(B)]

=[1-P(A)-P(B)+P(A∩B)]/[1-P(B)]

=( 1- 1/3 -1/2 + 1/8) /( 1- 1/2)

= 7/12