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# The standard deviation of a certain set of data is 3. If 20

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Current Student
Joined: 29 Jan 2005
Posts: 5218
The standard deviation of a certain set of data is 3. If 20 [#permalink]

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02 Oct 2005, 04:29
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The standard deviation of a certain set of data is 3. If 20 is 2 standard deviations away from the mean, which of the following values could be the mean of the set of data?

A. 14
B. 20
C. 24
D. 18
E. 25
VP
Joined: 13 Jun 2004
Posts: 1115
Location: London, UK
Schools: Tuck'08

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02 Oct 2005, 04:35
1 standard deviation is 3 units
so 2 standard deviations are 6 units

it could be 2 numbers :
20+6 = 26
OR
20-6 = 14

GMATT73, I can see that tonight you are on fire ! many questions
Manager
Joined: 25 Aug 2004
Posts: 169
Location: MONTREAL

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02 Oct 2005, 17:26
I agree with 14. It could be 26 too, but 26 is not from the answer choice...
Senior Manager
Joined: 15 Apr 2005
Posts: 415
Location: India, Chennai

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03 Oct 2005, 04:25
GMATT73 wrote:
The standard deviation of a certain set of data is 3. If 20 is 2 standard deviations away from the mean, which of the following values could be the mean of the set of data?

A. 14
B. 20
C. 24
D. 18
E. 25

1 sigma = 3, so 2 sigma = 6
20 is 2 sigma from the mean, so mean could be either 20 + 6 = 26 or
20-6 = 14. And hence A.
Current Student
Joined: 29 Jan 2005
Posts: 5218

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03 Oct 2005, 06:55
OA is A. Just curious, has anyone ever had to actually calculate standard deviation on an official test? Even if you are scoring towards the upper end of the spectrum??
Intern
Joined: 05 May 2005
Posts: 44

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03 Oct 2005, 12:15
don't quote me on this, but I highly doubt that we would have to calculate standard deviations for the GMAT
VP
Joined: 13 Jun 2004
Posts: 1115
Location: London, UK
Schools: Tuck'08

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03 Oct 2005, 20:00
The standard deviation calculation is not required in Gmat, however you should know the formula because it could help in some tough PS.
03 Oct 2005, 20:00
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