飞机被击落的概率为
0.4*0.5*0.7+0.6*(0.4*0.5*(1-0.7)+0.4*(1-0.5)*0.7+(1-0.4)*0.5*0.7)+0.2*(0.4*(1-0.5)*(1-0.7)+(1-0.4)*0.5*(1-0.7)+(1-0.4)*(1-0.5)*0.7)
=0.4*0.5*0.7+0.6*(0.4*0.5*0.3+0.4*0.5*0.7+0.6*0.5*0.7)+0.2*(0.4*0.5*0.3+0.6*0.5*0.3+0.6*0.5*0.7)
=0.14+0.246+0.072
=0.458懂了，谢谢