赢：0 1 2 3 4
得分：4 5 6 7 8
概率：(1/3)^4 4(1/3)³(2/3) 6(2/3)²(1/3)² 4(2/3)³(1/3) (2/3)^4
数学期望=4×(1/3)^4+5×4(1/3)³(2/3)+6×6(2/3)²(1/3)²+7×4(2/3)³(1/3)+8(2/3)^4
=(4+40+144+224+128)/81
=540/81谢谢！但赢一场的概率为什么是4(1/3)³(2/3) 而不是(1/3)³(2/3)？