Question on SD

[sankruth]

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

[StarDust845]

Is the answer E?

Calista.

[sankruth]

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!

[Stuart@KaplanGMAT]

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.

[sankruth]

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!