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# standard deviation-set of integers

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Manager
Joined: 16 May 2011
Posts: 204
Concentration: Finance, Real Estate
GMAT Date: 12-27-2011
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26 Jun 2011, 07:10
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Question Stats:

89% (01:21) correct 11% (00:41) wrong based on 9 sessions

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. If s, r, t, u are integers, which one has the same standard deviation as s, r, t, u ?
A. |s|, |r|, |t|, |u|
B. s+1, r+1, t+1, u+1
C. 2s+s, 2r+2, 2t+2, 2u+2
d. s^2+4, r^2+4, t^+4, u^2+4
[Reveal] Spoiler: OA
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Re: standard deviation-set of integers [#permalink]

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26 Jun 2011, 08:23
Clear B.

Adding or subtracting a constant from a set of numbers does not change the Standard Deviation
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Joined: 20 Dec 2010
Posts: 2010
Re: standard deviation-set of integers [#permalink]

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26 Jun 2011, 08:23
dimri10 wrote:
. If s, r, t, u are integers, which one has the same standard deviation as s, r, t, u ?
A. |s|, |r|, |t|, |u|
B. s+1, r+1, t+1, u+1
C. 2s+s, 2r+2, 2t+2, 2u+2
d. s^2+4, r^2+4, t^+4, u^2+4

I think the question should be: Which one MUST have the same std deviation?

"C" can be ruled out because when we multiply or divide every element of a set by a constant, the standard deviation also gets multiplied/divided by the same constant.

"D": If s,r,t,u are different integers; multiplying every element with different constant i.r. multiplying r with r, s with s; will affect the std deviation.

"A": 10, 12, -10, -12: Std Dev must be greater than 10, 12, 10, 12

"B": Irrespective of the values we associate with s,r,t and u; the std deviation will not change because adding or subtracting a constant from every element of the set has no effect on its std dev.

Also refer:
math-standard-deviation-87905.html
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Re: standard deviation-set of integers [#permalink]

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05 Jul 2011, 00:19
cool question and cool answers too
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Re: standard deviation-set of integers   [#permalink] 05 Jul 2011, 00:19
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