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Standard Deviation

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Standard Deviation [#permalink] New post 05 Nov 2007, 06:45
I am a struggling gmater with MATH.. desperately..... please help me again to understand why the answer is so..

Q. If a cetain 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?

1) 12.0
2) 13.5
3) 17.0
4) 23.5
5) 26.5

and the answer is 1)... please help me understand the solution...
Thank you for your sharings, in advance..
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 [#permalink] New post 05 Nov 2007, 06:48
2.5 SD = 2.5 * 3 = 7.5

more than 2.5 standard deviations from the mean is
either less than 20 - 7.5 = 12.5, or

greater than 20 + 7.5 = 27.5

So ans A
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so... [#permalink] New post 05 Nov 2007, 06:56
2.5 standard deviation from the mean
means
2.5 * SD??

Ah ah.. thank you.. so much..

sidbidus wrote:
2.5 SD = 2.5 * 3 = 7.5

more than 2.5 standard deviations from the mean is
either less than 20 - 7.5 = 12.5, or

greater than 20 + 7.5 = 27.5

So ans A
so...   [#permalink] 05 Nov 2007, 06:56
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