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by sankruth » Wed Jan 16, 2008 12:03 pm
If M is a negative integer and K is a positive integer, which of the following could be the Standard Deviation of the 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 StarDust845 » Wed Jan 16, 2008 12:09 pm
Is the answer E?

Calista.
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by sankruth » Wed Jan 16, 2008 12:25 pm
StarDust845 wrote:Is the answer E?

Calista.
Sorry, I forgot to ask the main question... Is there a way to solve it in under 2 minutes?

By the way E is correct!
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Re: Question on SD

by Stuart@KaplanGMAT » Wed Jan 16, 2008 12:33 pm
sankruth wrote:If M is a negative integer and K is a positive integer, which of the following could be the Standard Deviation of the 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
Just curious - where is this question from? I've never seen a GMAT question that asked the test taker to calculate SD.

On the other hand, we don't actually need to do any calcuations to answer this question, we just need to understand how SD works.

SD is a measurement of how spread out the members of a set are. Since SD really measures distance, there's no such thing as a negative SD.

Further, unless all the members of the set are identical, the SD will always be greater than 0.

So, we can't have negative SD, statements I and II are out. Some of the members of the set are different, so statement III is out. Pick (e), none of the above.
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by sankruth » Thu Jan 17, 2008 2:18 am
Sorry, I dont know the source of this question. Got a small set of questions on Statistics from a friend.

Thanks for your explanation, Stuart!
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