可能的组合:N代表没失火Y代表失火的机率NNNNNNNYNNYYNYYYYYYY机率是1*0.9^44*0.9^3*0.16*0.9^2*0.1^24*0.9*0.1^31*0.1^4损失的期望值:0.9^4*0+0.9^3*0.1*4*(50000/4)+0.9^2*0.1^2*6*(50000/4)+0.9*0.1^3*4*(50000/4)+0.1^4*50000=4302.5
