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# PS: standard deviations

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Intern
Joined: 21 Aug 2008
Posts: 23

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03 Dec 2008, 14:25
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For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

a) 74
b) 76
c) 78
d) 80
e) 82

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Director
Joined: 12 Jul 2008
Posts: 511
Schools: Wharton

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03 Dec 2008, 14:48
samlosco wrote:
For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

a) 74
b) 76
c) 78
d) 80
e) 82

A

Let m = mean
Let s = std dev

m = 58 + 2d
m = 98 - 3d

98 - 3d = 58 + 2d
5d = 40
d = 8

m = 58 + 2*8 = 58 + 16 = 74
SVP
Joined: 29 Aug 2007
Posts: 2420

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03 Dec 2008, 21:46
samlosco wrote:
For a certain examination, a score of 58 was 2 standard deviations below the mean, and a score of 98 was 3 standard deviations above the mean. What was the mean score for the examination?

a) 74
b) 76
c) 78
d) 80
e) 82

SD = (98 - 58)/5
SD = 8

58 = mean - 2 (SD)
mean = 58 + 2 (8)
mean = 74

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

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

GT

Re: PS: standard deviations &nbs [#permalink] 03 Dec 2008, 21:46
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