himba

1. P(A',B')<=min{P(A'),P(B')}=min{(1-0.5),(1-0.4)}=min{0.5,0.6}=0.5

so  0<=P{AB都不做}<=0.5

2.两次为8的组合为（0，8）,(1,7),(2,6),(3,5),(4,4),(5,3),(6,2),(7,1),(8,0)

so 出现过5的概率为2/9