=15*(0.6)^4(0.4)^2+6*(0.6)^5(0.4)+(0.6)^5(0.6) =15*(0.6)^4(0.4)^2+(2.4+0.6)(0.6)^5 =15*(0.6)^4(0.4)^2+3*(0.6)^5 =15*0.4*(0.6)^4*0.4+3*(0.6)^5 =6*0.4*(0.6)^4+3*(0.6)^5 =4*(0.6)^5+3*(0.6)^5 =7*(0.6)^5 完毕
