18.解:(1) 设从甲、乙、丙三台机床加工的零件中任取一件是一等品为事件A,B,C , 则 P(A)=0.7, P(B)=0.6, P(C)=0.8
从甲、乙、丙加工的零件中各取一件检验,至少有一件一等品的概率为
=1-0.3×0.4×0.2=0.976
4分
(2) 将三台机床加工的零件混合到一起,从中任意的抽取一件检验,它是一等品的概率为 P2=
8分
(3) P(X=4)=
×0.74=0.2401,
P(X=3)=
×0.3×0.73=0.4116
P(X=2)=
×0.32×0.72=0.2646, P(X=1)=
×0.33×0.7=0.0756
P(X=0)=
×0.34=0.0081
|
X |
4 |
3 |
2 |
1 |
0 |
|
P |
0.2401 |
0.4116 |
0.2646 |
0.0756 |
0.0081 |
X~B(4,0.7),所以EX=4×0.7=2.8 12分