∵n1=n6=1,
∴P(ξ=2)=
C | 04 |
2 |
3 |
16 |
81 |
C | 14 |
1 |
3 |
2 |
3 |
32 |
81 |
C | 24 |
1 |
3 |
2 |
3 |
8 |
27 |
C | 34 |
1 |
3 |
2 |
3 |
8 |
81 |
C | 44 |
1 |
3 |
1 |
81 |
∴ξ的分布列为:
∴ξ的数学期望为Eξ=2×
16 |
81 |
32 |
81 |
24 |
81 |
8 |
81 |
1 |
81 |
10 |
3 |
2 |
3 |
1 |
3 |
C | 04 |
2 |
3 |
16 |
81 |
C | 14 |
1 |
3 |
2 |
3 |
32 |
81 |
C | 24 |
1 |
3 |
2 |
3 |
8 |
27 |
C | 34 |
1 |
3 |
2 |
3 |
8 |
81 |
C | 44 |
1 |
3 |
1 |
81 |
16 |
81 |
32 |
81 |
24 |
81 |
8 |
81 |
1 |
81 |
10 |
3 |