虽然有人已答我还是详细讲解一下思路,
至多有一台需要维修 ,则有四种情况,只有甲维修,只有乙维修,只有丙维修
或是甲乙丙都不需要维修,
p=0.1(1-0.2)(1-0.15）+0.2(1-0.1)(1-0.15)
+0.15(1-0.1)(1-0.2) +(1-0.1)(1-0.2)(1-0.15)
=0.068+0.153+0.108+0.612
=0.931