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# M25 - Question #10

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Intern
Joined: 26 Aug 2009
Posts: 22

Kudos [?]: 4 [0], given: 3

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30 Oct 2009, 09:32
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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Kudos [?]: 4 [0], given: 3

Manager
Affiliations: CFA Level 2 Candidate
Joined: 29 Jun 2009
Posts: 220

Kudos [?]: 283 [0], given: 2

Schools: RD 2: Darden Class of 2012
Re: M25 - Question #10 [#permalink]

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30 Oct 2009, 12:02
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.

Kudos [?]: 283 [0], given: 2

VP
Joined: 05 Mar 2008
Posts: 1468

Kudos [?]: 300 [0], given: 31

Re: M25 - Question #10 [#permalink]

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31 Oct 2009, 17:52
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

Kudos [?]: 300 [0], given: 31

SVP
Joined: 29 Aug 2007
Posts: 2472

Kudos [?]: 843 [0], given: 19

Re: M25 - Question #10 [#permalink]

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02 Nov 2009, 22:29
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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Kudos [?]: 843 [0], given: 19

Intern
Joined: 12 Sep 2009
Posts: 18

Kudos [?]: 16 [0], given: 2

Re: M25 - Question #10 [#permalink]

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03 Nov 2009, 06:59
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.

Kudos [?]: 16 [0], given: 2

VP
Joined: 05 Mar 2008
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Kudos [?]: 300 [0], given: 31

Re: M25 - Question #10 [#permalink]

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03 Nov 2009, 08:16
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

Kudos [?]: 300 [0], given: 31

Manager
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Re: M25 - Question #10 [#permalink]

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04 Nov 2009, 03:39
3
KUDOS
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

Kudos [?]: 294 [3], given: 25

SVP
Joined: 29 Aug 2007
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Kudos [?]: 843 [0], given: 19

Re: M25 - Question #10 [#permalink]

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04 Nov 2009, 21:19
+1 for Tip for the day:

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

_________________

Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html

GT

Kudos [?]: 843 [0], given: 19

Re: M25 - Question #10   [#permalink] 04 Nov 2009, 21:19
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# M25 - Question #10

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