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标题: 请教两道PREP的数学题，望指点 [打印本页]

作者: susan_shuxin 时间: 2008-1-3 22:37
标题: 请教两道PREP的数学题，望指点

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During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?

(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.

(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.

这道题答案是A，我没看懂题目的意思，希望大家帮忙翻译下，谢谢

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For the students in class A, the range of their heights is r centimeters and the greatest height is g centimeters. For the students in class B, the range of their heights is s centimeters and the greatest height is h centimeters. Is the least height of the students in class A greater than the least height of the students in class B ?

(1) r < s

(2) g > h

答案是C，想问的是其他人的身高分布都没有说怎么就能确定最矮的呢？难道只有两个人？

作者: shijiu86 时间: 2008-1-3 22:52
第一题定理 6个水箱按比例取水标准差不会变条件2没用所以选A 第2题没什么问题,the range of their heights is r centimeters and the greatest height is g centimeters 意思是全班身高的范围是R厘米最高的是G厘米那么最矮的就是G-R厘米拉同理 B班就是H-S厘米咯明白没那就选C了个人观点不知道对不对有错高手请指点

作者: ciscogeek 时间: 2008-1-3 22:53

1，标准方差。大家去掉30% 方差应该不变。所以选A.

2. r < g
s < h

r <s< h< g

所以比出来第二组最矮的比第一组最矮的要高。

作者: susan_shuxin 时间: 2008-1-4 17:11
恩，恩，懂了，谢谢shijiu86和ciscogeek,Thanks a lot!

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