(1)乙取胜
后面甲最多赢一局(前6局里面)
P=C(4,4)(1/2)^4+C(4,1)(1/2)^5=3/16
(2)P=C(4,1)(1/2)^5+c(4,1)(1/2)^5=1/4
(3)ε=4,5,6,7
P(ε=4)=(1/2)^2=1/4
P(ε=5)=C(2,1)(1/2)^3=1/4
P(ε=6)=C(4,4)(1/2)^4+c(3,1)(1/2)^4=1/4
P(ε=7)=C(4,1)(1/2)^5+c(4,1)(1/2)^5=1/4
Eε=5.5
要进行5局,乙在前4局赢了1局,前2局甲赢了,所以乙在3,4局中胜一局
C(4,4)(1/2)^4乙连下4局
c(3,1)(1/2)^4 甲在3,4,5中赢1局,第六句甲必赢