| ||||
|
| 8 |
| 15 |
解得n=6，n=4（舍去），
∴该小组中有6个女生；
（2）由题意，ξ的取值为0，1，2，3；
P（ξ=0）=
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 36 |
P（ξ=1）=
| C | 12 |
| 2 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 3 |
| 3 |
| 4 |
| 7 |
| 36 |
P（ξ=3）=(
| 2 |
| 3 |
| 3 |
| 4 |
| 12 |
| 36 |
P（ξ=2）=1-
| 1 |
| 36 |
| 7 |
| 36 |
| 12 |
| 36 |
| 16 |
| 36 |
∴ξ的分布列为：
| ξ | 0 | 1 | 2 | 3 | ||||||||
| P |
|
|
|
|
| 7 |
| 36 |
| 16 |
| 36 |
| 12 |
| 36 |
| 25 |
| 12 |
| 8 |
| 15 |
| 3 |
| 4 |
| 2 |
| 3 |
| ||||
|
| 8 |
| 15 |
| 1 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 36 |
| C | 12 |
| 2 |
| 3 |
| 1 |
| 3 |
| 1 |
| 4 |
| 1 |
| 3 |
| 3 |
| 4 |
| 7 |
| 36 |
| 2 |
| 3 |
| 3 |
| 4 |
| 12 |
| 36 |
| 1 |
| 36 |
| 7 |
| 36 |
| 12 |
| 36 |
| 16 |
| 36 |
| ξ | 0 | 1 | 2 | 3 | ||||||||
| P |
|
|
|
|
| 7 |
| 36 |
| 16 |
| 36 |
| 12 |
| 36 |
| 25 |
| 12 |