题目
题型:不详难度:来源:
(1)所选3人中女生人数为
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083938-65445.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083938-65445.png)
(2)在男生甲被选中的情况下,求女生乙也被选中的概率.
答案
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083938-29411.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-69434.png)
解析
试题分析:(1)ξ得可能取值为 0,1,2,3
由题意P(ξ=0)=
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-29974.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-48162.png)
P(ξ=2)=
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-52033.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-35148.png)
因此,由公式计算即得 Eξ.
(2)男生甲被选中的种数为
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-11681.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-61582.png)
由古典概型概率的计算即得.
(1)ξ得可能取值为 0,1,2,3
由题意P(ξ=0)=
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-29974.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-48162.png)
P(ξ=2)=
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-52033.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-35148.png)
∴ξ的分布列、期望分别为:
ξ | 0 | 1 | 2 | 3 |
p | ![]() | ![]() | ![]() | ![]() |
Eξ=0×
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083941-40357.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083941-20009.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083941-60346.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083941-49688.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083938-29411.png)
(2)设在男生甲被选中的情况下,女生乙也被选中的事件为C
男生甲被选中的种数为
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-11681.png)
种数为
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083940-61582.png)
∴P(C)=
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083942-37763.png)
在男生甲被选中的情况下,女生乙也被选中的概率为
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083939-69434.png)
核心考点
试题【第十二届全国人民代表大会第二次会议和政协第十二届全国委员会第二次会议,2014年3月在北京召开.为了做好两会期间的接待服务工作,中国人民大学学生实践活动中心从7】;主要考察你对离散型随机变量及其分布列等知识点的理解。[详细]
举一反三
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083925-89131.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083925-65034.png)
求甲在4局以内(含4局)赢得比赛的概率;
记
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083925-59337.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083925-59337.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083918-15695.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083918-68429.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083919-64161.png)
A.![]() | B.![]() | C.![]() | D.![]() |
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083904-61994.png)
![](http://img.shitiku.com.cn/uploads/allimg/20191027/20191027083904-61994.png)