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# M25 - Question #10

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Intern
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30 Oct 2009, 08:32
Forgive me if I am wrong, but I truly believe the answer to this question to be "D."

Is the standard deviation of T positive?

Well,... stem question #1 clearly states that all elements of set T are positive. Thus, it is given that the ultimate standard deviation of set T is, in fact, positive.

Am I wrong?
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Manager
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Re: M25 - Question #10 [#permalink]

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30 Oct 2009, 11:02
A doesn't necessarily need to hold true.

If your data contain all the same number your standard deviation would be 0 which is not a positive number.

In B we know that the standard deviation is = 0 (range is 0) and therefore it is not positive.
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Re: M25 - Question #10 [#permalink]

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31 Oct 2009, 16:52
we are never told how many numbers are contained in the set. The standard deviation is zero if there is one number or all the numbers are the same
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Re: M25 - Question #10 [#permalink]

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02 Nov 2009, 21:29
stilite wrote:
Forgive me if I am wrong, but I truly believe the answer to this question to be "D."

Is the standard deviation of T positive?

Well,... stem question #1 clearly states that all elements of set T are positive. Thus, it is given that the ultimate standard deviation of set T is, in fact, positive.

Am I wrong?

1. Positive (+ve) elements (of the set) come in at least two flavors: (1, 1, 1, 1, 1, 1) or (2, 4, 5, 66, 77, 100).
In first case, SD is 0 where as in second case, SD is +ve. NSF.

2. Range is zero means, the elements of the set are same irrespective of signs. So SD is always 0. SUFF.
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Re: M25 - Question #10 [#permalink]

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03 Nov 2009, 05:59
Per the OG, '0' is neither +ve nor -ve, how come 2 is sufficient? The questions is asking if the SD of T is +ve... Correct me if I'm wrong.
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Re: M25 - Question #10 [#permalink]

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03 Nov 2009, 07:16
seluka wrote:
Per the OG, '0' is neither +ve nor -ve, how come 2 is sufficient? The questions is asking if the SD of T is +ve... Correct me if I'm wrong.

The range is 0 therefore the SD is 0

0 is neither positive nor negative

The question is asking if the SD is positive...but as you said it's neither...so the answer is sufficient that the SD is not positive

It's a yes/no answer. In this case, no
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Re: M25 - Question #10 [#permalink]

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04 Nov 2009, 02:39
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Hi guys, the answer is definitely B

A gives 2 answers (As expressed in the solution) - set (6,6) will have range 0 (therefore not positive). Similarly, set (6,12) will have range 6 (positive)

Every set(excepting as set containing same numbers) will have a positive S.D.

The key to solving most gmatclub test questions is to pay attention to detail
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Re: M25 - Question #10 [#permalink]

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04 Nov 2009, 20:19
+1 for Tip for the day:

zaarathelab wrote:
The key to solving most gmatclub test questions is to pay attention to detail

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Re: M25 - Question #10   [#permalink] 04 Nov 2009, 20:19
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# M25 - Question #10

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