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# For an examination, a score of 58 was two standard

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Intern
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For an examination, a score of 58 was two standard [#permalink]  14 Oct 2008, 14:44
For an examination, a score of 58 was two standard deviations below the mean and a score of 98 was three standard deviations above the mean. What was the mean score for the examination?

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

Thanks.
Director
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Re: Standard Deviation [#permalink]  14 Oct 2008, 14:59
let the mean = y
let stand dev= x

y + 3x =98
y - 2x = 58

subtract second equation from first

5x=40, x=8

2(8) + 58 = 74

or

58-98=40

40 represents 5 standard deviations

so 40/5 =8

2(8) + 58 = 74
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Re: Standard Deviation [#permalink]  14 Oct 2008, 15:03
A
Will go with the explanation of bigtreezl
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Re: Standard Deviation [#permalink]  14 Oct 2008, 15:17
Poots wrote:
For an examination, a score of 58 was two standard deviations below the mean and a score of 98 was three standard deviations above the mean. What was the mean score for the examination?

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

Thanks.

-A + 2S = -58
A+3S =98

5S = 40

S = 8

A = 74

A
Intern
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Re: Standard Deviation [#permalink]  14 Oct 2008, 16:11
Both explanations are great! Thanks so much.
Re: Standard Deviation   [#permalink] 14 Oct 2008, 16:11
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