Question

英语概率题求助！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！

A student estimates that the probability of his
passing Chemistry or English is 0.8, the probability
of his passing Chemistry is 0.7, but his
probability of passing both is 0.5. What should
be his estimate of the probability of his passing
English?

Answer 1

P(A∪B)=P(A)+P(B)-P(A∩B)
If event A represents pass chem
event B represents pass Eng
then we have

P(A∪B)=0.8
因为是或的关系即，过化学或者过英语，即至少过一门即可
即过化学的事件发生+过英语的时间发生
=过化学的事件集并上过英语的事件集
=A∪B

P(A)=0.7
P(A∩B)=0.5

so the equation becomes
0.8=0.7+P(B)-0.5
P(B)=0.6
the probability of his passing
English is 0.6

Answer 2

0.6
画一个文氏图，很容易的。

追问

请求过程好吗？交集是0.5，但是0.8不理解

追答

用c表示C中不属于公共部分的。p(c)+p(both)=p(C)=0.7;p(c)=0.2;p(c)+p(both)+p(e)=0.8=0.2+0.5+p(e) ; p(e)=0.1;p(E)=p(both)+p(e)=0.6;e表示E中不属于公共的部分概率