先求A1、A2的故障率A1=B1*B2=0.1*0.05=0.005
A2=B3*B4=0.05*0.1=0.005
求T的事故率可用两种方法：
方法一：T=A1*(1-A2)+A2*(1-A1)+A1*A2
=0.005*0.995+0.005*0.995+0.005*0.005
=0.009975
≈0.01
方法二：T=1-(1-0.005)(1-0.005)
=1-0.990025
=0.00975
