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标题: [求助]一道PREP数学，请教各位！ [打印本页]

作者: xiaoxique89 时间: 2009-11-4 06:43 标题: [求助]一道PREP数学，请教各位！

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than

2.5 standard deviations from the mean?

(A) 12.0

(B) 13.5

(D) 23.5

(E) 26.5

答案选A，没有读懂题。

作者: chenholan 时间: 2009-11-5 06:48

standard deviation标准差
1 standard deviations from the mean就是mean+standard deviation
2.5 standard deviations from the mean就是mean+2.5standard deviation
不在这个范围的（就是大于+2.5，小于-2.5）就是大于2.5 standard deviations from the mean。

作者: Kanewu 时间: 2009-11-9 09:45

QUOTE:

以下是引用chenholan在2009-11-5 6:48:00的发言：
standard deviation标准差
1 standard deviations from the mean就是mean+standard deviation
2.5 standard deviations from the mean就是mean+2.5standard deviation
不在这个范围的（就是大于+2.5，小于-2.5）就是大于2.5 standard deviations from the mean。

agree

作者: poorleafer 时间: 2009-11-11 20:14

sd = 3
2.5 * sd = 7.5
20 + 7.5 = 27.5 and 20 - 7.5 = 12.5, the question is asking for a number that's outside of this range (12.5 - 27.5)....so A is correct.

作者: xiaoxique89 时间: 2009-11-12 07:02

明白了，谢谢各位！

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