由等可能性事件的概率公式得
P(ξ=0)=
25 |
35 |
32 |
243 |
| ||
35 |
80 |
243 |
P(ξ=2)=
| ||
35 |
80 |
243 |
| ||
35 |
40 |
243 |
P(ξ=4)=
| ||
35 |
10 |
243 |
1 |
35 |
1 |
243 |
∴ξ的分布列为
∴Eξ=0×
32 |
243 |
80 |
243 |
80 |
243 |
40 |
243 |
10 |
243 |
1 |
243 |
405 |
243 |
5 |
3 |
故选C.
1 |
3 |
4 |
3 |
7 |
3 |
5 |
3 |
2 |
3 |
25 |
35 |
32 |
243 |
| ||
35 |
80 |
243 |
| ||
35 |
80 |
243 |
| ||
35 |
40 |
243 |
| ||
35 |
10 |
243 |
1 |
35 |
1 |
243 |
32 |
243 |
80 |
243 |
80 |
243 |
40 |
243 |
10 |
243 |
1 |
243 |
405 |
243 |
5 |
3 |