1 Ex=2 Ey=6*1/2=3 E(X-Y)=(-1)
2 P(A∪B)=Pa+Pb-Pab=0.6 Pab=0 Pb=0.4
3 P(b/a)=P(ba)/P(a)=0.3 P(ab)=0.03
o表示发生洪水
p(o)=p(a)+P(b)-p(ab)=0.27
p(a/b)=p(ab)/p(b)=0.15
1 Ex=2 Ey=6*1/2=3 E(X-Y)=(-1)
2 P(A∪B)=Pa+Pb-Pab=0.6 Pab=0 Pb=0.4
3 P(b/a)=P(ba)/P(a)=0.3 P(ab)=0.03
o表示发生洪水
p(o)=p(a)+P(b)-p(ab)=0.27
p(a/b)=p(ab)/p(b)=0.15