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If M is a negative integer

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by CSASHISHPANDAY » Mon Dec 03, 2012 9:22 pm
If M is a negative integer and K is a positive integer, which of the following could be the standard deviation of a set {-7, -5, -3, M, 0, 1, 3, K, 7}

I. -1.5 II. -2 III. 0
(A) I only (B) II only (C) III only (D) I and III only (E) None
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by Brent@GMATPrepNow » Mon Dec 03, 2012 9:42 pm
CSASHISHPANDAY wrote:If M is a negative integer and K is a positive integer, which of the following could be the standard deviation of a set {-7, -5, -3, M, 0, 1, 3, K, 7}

I. -1.5 II. -2 III. 0
(A) I only (B) II only (C) III only (D) I and III only (E) None
Nice question. I like how the information regarding M and K is totally superfluous :-)

Okay, first we need to recognize that the standard deviation of any set of numbers will always be greater than or equal to zero.

So, the standard deviation can never equal -1.5 or -2.

Also, the only time that the standard deviation equals zero is when all of the numbers in the set are equal. Since the numbers in this set are not all equal, the standard deviation cannot be zero.

If the standard deviation cannot equal -1.5, -2, or 0, the correct answer here is E

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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by CSASHISHPANDAY » Thu Dec 06, 2012 10:01 pm
Thanks Brent
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