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gmat prep - SD, Mean

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Junior | Next Rank: 30 Posts
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by steinbock » Mon Jun 02, 2008 7:37 am
Another one:

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
C) 17.0
D) 23.5
E) 26.5

OA is A
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by VP_RedSoxFan » Mon Jun 02, 2008 8:58 am
If the SD is 3.0 and we're looking for the answer choice that is 2.5 stdevs from the mean, then we're looking for an answer choice that is less than 20 - 3*2.5 = 12.5 or greater than 20 + 3*2.5 = 27.5.

Only [A] fits the bill here.

Hope this helps, good luck.
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Range

by vladmire » Sun Nov 02, 2008 12:38 pm
Are there any other ways to come to the same answer. The question asks which value is more than 2.5sd away from the mean. So I will never come up with exactly 12?
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by cramya » Sun Nov 02, 2008 1:50 pm
Vladimire,
More than 7.5

Eg: 20-7.5 = 12.5

12 is more than 2.5sd away from the mean.

Lets say choice A was 28 instead of 12 then this would work too since its more than 2.5sd(2.5*3) away

Hope this helps!
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