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SLIDE #33 in the FlashCards. Standard Deviation

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SLIDE #33 in the FlashCards. Standard Deviation [#permalink] New post 09 Oct 2011, 09:55
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First of all, I would like to thank all of the GMAT Club team for the amazing effort and dedication it continues to show.
I personally get motivated when I read about the successful GMAT journeys and their after math.

I have a question regarding one of the Standard Deviation examples mentioned in Flash Cards (Slide #33)

What is the Standard Deviation of a set of consecutive even integers?
(1) There are 39 elements in the set.
(2) the mean of the set is 382

[Reveal] Spoiler: Doubt
The answer is A, statement (1) is sufficient.

Can some one please explain the logic behind it. I mean how can we get the S.D with out having the actual elements?

Thanks in advance
[Reveal] Spoiler: OA
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Re: SLIDE #33 in the FlashCards. Standard Deviation [#permalink] New post 09 Oct 2011, 18:48
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I think you missed something in the text as we CAN actually find out the members of the set.

We know that they are consecutive even integers and the mean is 382. That means there are 19 consecutive even integers on the left of this number and another 19 on the right (39 - 1 = 38) and 38/2 = 19.

However in this case, you don't really need to know the actual members of the set since the standard deviation would be known by default regardless of the number values (2, 4, 6, etc) or (20224, 20226, etc). We know that they are spaced within 39*2 = 78 of each other and that's all we need to know. We don't need to calculate the details.

Hope this helps.
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Re: SLIDE #33 in the FlashCards. Standard Deviation   [#permalink] 09 Oct 2011, 18:48
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SLIDE #33 in the FlashCards. Standard Deviation

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