有效率=0.95无效率=1-0.95=0.05X: 治愈人数X~B(10,0.95)P(至少有8人治愈)=P(8人治愈)+P(9人治愈)+P(10人治愈)=P(X=8)+P(X=9)+P(X=10)=(10C8)(0.95)^8.(0.05)^2 +(10C9)(0.95)^9.(0.05)+(10C10)(0.95)^10
