设篮球队甲和乙进行比赛,若有一队胜4场则比赛结束.如果甲和乙在每场比赛中获胜的概率都是1/2,

比赛场数X 概率P
4 (1/2)^4*2=1/8
5 (C(4,3)*(1/2)^3*(1/2)*(1/2))*2=1/4
6 (C(5,3)*(1/2)^3*(1/2)^2*(1/2))*2=5/16
7 (C(6,3)*(1/2)^3*(1/2)^3*(1/2))*2=5/16
比赛场数的数学期望
E=4*1/8+5*1/4+6*5/16+7*5/16=(8+20+30+35)/16=93/16=5.8125