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1 KUDOS received
Intern
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Joined: 18 May 2011
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Kudos [?]: 1 [1] , given: 13

SD [#permalink] New post 29 May 2011, 10:16
1
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A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

75% (01:51) correct 25% (00:40) wrong based on 4 sessions
Hi All,
I chose C for this one but the correct answer is A. Can someone please help explain why? :roll:

Thanks!
[Reveal] Spoiler: OA

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Math Forum Moderator
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Kudos [?]: 902 [0], given: 376

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Re: SD [#permalink] New post 29 May 2011, 11:38
Carol680 wrote:
Hi All,
I chose C for this one but the correct answer is A. Can someone please help explain why? :roll:

Thanks!


Please search before posting. Almost all gmatprep questions are already discussed.

Refer:
gmat-prep-ds-q-94166.html
math-standard-deviation-87905.html
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Intern
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Joined: 18 May 2011
Posts: 17
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Kudos [?]: 1 [0], given: 13

Re: SD [#permalink] New post 01 Jun 2011, 01:57
thangduong wrote:
it is best to remember the formular of the SD= square of (1/n (a1-x)^2 + (a2-x)^2+.........)

from 1, now we replace a1 with 0.7 a1, x with 0.7 x as condition 1 tell us. Every thing reduce to 0.7

it is clear we can find new SD. DONT COUNT, just know it is sufficient.

from 2, we can not know the square of diffence between each number and average in the new set. not sufficient.


thank you very much :)
Re: SD   [#permalink] 01 Jun 2011, 01:57
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