10电影票抽奖技巧视频

A2={第一个人没拿到电影票}

B={第二个人拿到电影票}

P(A1)=6/10

P(A2)=4/10

P(B|A1)=5/9

P(B|A2)=6/9

P(B)= P(a 1)P(B | a 1)+P(a 1)P(B | a 1)

=6/10 5/9+4/10 6/9

=54/90

=3/5