0.8x0.7x（1-0.6）0.6x0.7x（1-0.8）0.7x（1-0.6）x（1-0.8）0.8x0.7x0.6
(1)为0.8*0.7*0.4=0.224.(2)为0.2*0.7*0.6=0.084.(3)为0.2*0.7*0.4=0.056.(4)为0.8*0.7*0.6=0.336.
