题干

2013年湛江市某校为了了解400名学生体育加试成绩,从中抽取了部分学生的成绩(满分为40分,而且成绩均为整数),绘制了频数分布表与频数分布直方图(如图),请结合图表信息解答下列问题:

(1)补全频数分布表与频数分布直方图;

(2)如果成绩在31分以上的同学属于优良请你估计全校约有多少人达到优良水平;

(3)加试结束后,校长说:“2011年,初一测试时,优良人数只有90人,经过两年的努力,才有今天的成绩….”假设每年优良人数增长速度一样,请你求出每年的平均增长率(结果精确到1%).

分组

频数

频率

15.5﹣20.5

6

0.10

20.5﹣25.5

 12 

0.20

25.5﹣30.5

18

0.30

30.5﹣35.5

15

 0.25 

35.5﹣40.5

9

0.15

合计


1.00

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答案(点此获取答案解析)

解:(1)由题意可得出:6÷0.10=60(人),
则60×0.2=12(人),1560
=0.25,
补全频数分布表与频数分布直方图如图所示:

同类题2

阅读下列短文,从每题所给的A、B、C和D项中,选出最佳选项。

Guilin is my favorite city in China because of its beauty, its waterways, its cafes, and most of all because I met my wife there. It is her hometown and we will both retire there in a few years.

Not only is Guilin a fascinating city, there are many interesting places to visit within a short drive from there. The Ling (sometimes called Lingqu) canal is the oldest canal in the world. It was built about 2,200 years ago and connects two major river systems, the Yangtze (to the east) and the Pearl River.

Longsheng Rice Terraces (龙胜梯田) is another manmade wonder that was built around 650 years ago. I have some photos of both of these places in my China Daily homepage Albums. Gudong Waterfall Park(古东瀑布) is another attraction that is worth visiting. The hike to the top of all these waterfalls isn’t very difficult and if you want, you can take a ride to the bottom on a personal rail car whose speed you can control with a brake.

If you want you can also climb up some of the waterfalls with the help of chains that are placed for the convenience of amateur climbers.

I have only been in Guilin during the winter and spring but my wife tells me it gets pretty hot in the summertime. That’s OK because I grew up in the Midwest of the US where it gets very hot and humid during the summer months. It rarely freezes in the winter and the spring and autumn are pleasant. Guilin receives a lot of rain, especially in late spring and early summer. Because of this there is lush(多汁的) plant life and many large trees in the area. 

Being from California I’m used to having a car to get around. In fact, it’s practically a necessity in California. But in Guilin almost everything is within walking distance and if you need to go further, public buses are available every five minutes on the busy streets and every 10-15 minutes just about everywhere else. There are plenty of taxis too and most trips are only six yuan.

It’s a perfect place to retire.