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The standard deviation of which of the following is equivale

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by vinni.k » Tue Jan 16, 2018 8:37 am
The standard deviation of which of the following is equivalent to that of {m, r, p, n}?

A. 2m,2r,2p,2n
B. m+2,r+2,p+2,n+2
C. |m|,|r|,|p|,|n|
D. 1/m, 1/r, 1/p, 1/n
E. {m^2, r^2, p^2, n^2}

OA is B

I got this question, but i am not sure how to eliminate C. I plug in some values for m,r,p,n such as -8,-6,-4,-2. After calculating for C, I think it's SD is equivalent to {m, r, p, n}.
Kindly help.

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by GMATGuruNY » Tue Jan 16, 2018 8:49 am
vinni.k wrote:The standard deviation of which of the following is equivalent to that of {m, r, p, n}?

C. |m|,|r|,|p|,|n|

i am not sure how to eliminate C. I plug in some values for m,r,p,n such as -8,-6,-4,-2. After calculating for C, I think it's SD is equivalent to {m, r, p, n}.
Original set:
-1, -1, 1, 1.
Option C yields the following set:
1, 1, 1, 1.
The SD of the red set is 0, since the four values are all the same.
The SD of the blue set is NOT 0, since the four values are NOT all the same.
Eliminate C.
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by vinni.k » Tue Jan 16, 2018 9:22 am
GMATGuruNY wrote: Original set:
-1, -1, 1, 1.
Option C yields the following set:
1, 1, 1, 1.
The SD of the red set is 0, since the four values are all the same.
The SD of the blue set is NOT 0, since the four values are NOT all the same.
Eliminate C.
It is a good example. Now, i wonder why it didn't come to my mind.
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by Jeff@TargetTestPrep » Mon Feb 26, 2018 10:43 am
vinni.k wrote:The standard deviation of which of the following is equivalent to that of {m, r, p, n}?

A. 2m,2r,2p,2n
B. m+2,r+2,p+2,n+2
C. |m|,|r|,|p|,|n|
D. 1/m, 1/r, 1/p, 1/n
E. {m^2, r^2, p^2, n^2}
We can adhere to the rule that when a constant is added to or subtracted from all the data points in a set, the standard deviation doesn't change.

Thus, the standard deviation of m, r, p, n is the same as the standard deviation of m+2, r+2, p+2, n+2.

Answer:B

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