问题 选择题

对于样本频率分布直方图与总体密度曲线的关系,下列说法正确的是(  )

A.频率分布直方图与总体密度曲线没有关系

B.频率分布直方图就是总体密度曲线

C.样本容量很大的频率分布直方图就是总体密度曲线

D.如果样本容量无限大,分组的组距无限减小,那么频率分布直方图就会无限接近总体密度曲线

答案

如果样本容量越大,所分组数越多,频率分布直方图中表示的频率分布就越接近于总体在各个小组内所取值的个数与总数比值的大小.

频率分布直方图与总体密度曲线是有关系的,故选项A不正确,

频率分布直方图不是总体密度曲线,故选项B不正确,

样本容量很大的频率分布直方图就越接近与总体密度曲线,故选项C不正确

设想如果样本容量不断增大,分组的组距不断缩小,则频率分布直方图实际上越来越接近于总体的分布,它可以用一条光滑曲线y=f(x)来描绘,这条光滑曲线就叫做总体密度曲线.总体密度曲线精确地反映了一个总体在各个区域内取值的规律.选项D正确

故选:D

阅读理解

The week after Jane's birthday, Barbara and Mary were away. Jane decided to have a late birthday party. She telephoned several friends. She asked some to bring records, some to bring food and others to bring something to drink. She rang another friend to see if she could borrow his record player. She herself bought some food and drink to get the party going. She took up all the carpets (地毯) so that they could dance. She did not know whether Barbara and Mary would have approved (赞成), but as long as she was careful, she was sure that they would not mind. She warned the two people in the flat above and invited them down. 

“Oh, ” said Jane, surprised. “What's all this about? ”

The first guests arrived soon after eight. The music was soon playing loudly and they started dancing. Some of Jane's friends brought other friends with them. As more and more people arrived,the noise increased. People started shouting at each other, so they turned the music up. This made it more difficult to hear each other above the music, so they shouted more loudly. At half past ten the bell rang. “Turn down the music!” someone shouted. “Someone probably called the police.” When Jane opened the door, there was a policeman standing there. She started to apologize, “I'm sorry about all the noise, officer. But you see, it was my birthday last week and I'm having a party.” “Never mind about that, miss. We're here because of something much more important.”

“Well, there's been a report of burglary (盗窃行为). We think the thief may have come to your party, pretending to be a friend of someone here. ”

小题1:When did Jane have the party?

A.On her birthday.

B.After her birthday.

C.Before Barbara and Mary left.

D.As soon as she telephone her friends.小题2:Why did people shout at each other at the party?

A.They got rather angry with each other.

B.They were very glad to make new friends.

C.They became too excited while dancing.

D.They couldn't hear each other because of the music.小题3:What reason did Jane think the policeman came for?

A.They made too much noise.   

B.A thief was among the guests.

C.He had some important things to do.

D.He was interested in birthday parties.

多项选择题