题干

2016年微信用户数量统计显示,微信注册用户数量已经突破9.27亿.微信用户平均年龄只有26岁,97.7%的用户在50岁以下,86.2%的用户在18﹣36岁之间.为调查大学生这个微信用户群体中每人拥有微信群的数量,现从北京市大学生中随机抽取100位同学进行了抽样调查,结果如下:

微信群数量

频数

频率

0至5个

0

0

6至10个

30

0.3

11至15个

30

0.3

16至20个

a

c

20个以上

5

b

合计

100

1

(Ⅰ)求a,b,c的值;

(Ⅱ)若从这100位同学中随机抽取2人,求这2人中恰有1人微信群个数超过15个的概率;

(Ⅲ)以这100个人的样本数据估计北京市的总体数据且以频率估计概率,若从全市大学生中随机抽取3人,记X表示抽到的是微信群个数超过15个的人数,求X的分布列和数学期望EX.

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    I had an experience once which taught me something about the ways people made a bad situation worse by blaming themselves. One January, I officiated (主持) at two funerals for two elderly women.____At the first home, the son of the deceased (已故) woman said, “If only I had sent my mother to Florida and gotten her out of this cold and snow, she would be alive today. It's my fault that she died.” At the second home, the son said, “If only I had not insisted her going to Florida, she would be alive today.____ It is my fault.”

    When things don't turn out as we would like them to, we tend to assume that had we done things differently, the story would have had a happier ending. Any time there is a death, the survivors will feel guilty. Because the course of action they took turned out bad, they believe that the opposite course, for example, keeping mother at home, would have turned out better.____

    There seem to be two elements involved in our readiness to feel guilty. The first lies in our belief that the world makes sense—there is a reason for everything that happens.

    The second is the thought that we are the cause of what happens, especially the bad things that happen.____A baby comes to think that the world exists to meet his needs, and that he makes everything happen in it. He wakes up in the morning and calls the rest of the world to its tasks.____When he is hungry, people feed him, and when he is wet, people change him. Very often, we do not completely abandon that childish thought that our wishes cause things to happen.

A. That long airplane ride was more than she could take.

B. After all, how could it have turned out any worse?

C. Life and dead is an unsolved mystery.

D. The roots of this feeling may lie in our childhood.

E. He cries, and someone comes to attend to him.

F. Both died a natural death.

G. They believe that they are responsible for what has happened.