设闯过成功记为1,失败记为0,不需要记为x.则闯关所有成功情况:
11xxx概率为 0.5*0.5 =0.25
1011x 0.5*0.5*0.5*0.5 =0.0625
10011 0.5*0.5*0.5*0.5*0.5=0.03125
011xx 0.5*0.5*0.5 =0.125
01011 0.5*0.5*0.5*0.5*0.5=0.03125
0011x 0.5*0.5*0.5*0.5 =0.0625
00011 0.5*0.5*0.5*0.5*0.5=0.03125
右侧数字全部相加,得0.59375