P(AB)=P(B|A)*P(A)=0.8*0.5=0.4,
P(A补交B)=P(B) - P(AB)= 0.2
P(A补并B)=P(A补)+P(B)-P(A补交B)= 1- 0.5 + 0.6 - 0.2= 0.9