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PS : Mean & SD

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PS : Mean & SD [#permalink]

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New post 17 Aug 2010, 11:35
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If a sample of data has mean of 20 and SD of 3, which of the following values is more than 2.5 SDs from the mean?

a. 12
b. 13.5
c. 17
d. 23.5
e. 26.5
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Re: PS : Mean & SD [#permalink]

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New post 17 Aug 2010, 11:43
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EnterMatrix wrote:
If a sample of data has mean of 20 and SD of 3, which of the following values is more than 2.5 SDs from the mean?

a. 12
b. 13.5
c. 17
d. 23.5
e. 26.5


Value is more than 2.5SD from the mean means that the distance between the mean and the value must be more than 2.5SD=7.5. So the value either <20-7.5=12.5 or >20+7.5=27.5.

Answer: A.
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Re: PS : Mean & SD [#permalink]

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New post 17 Aug 2010, 11:48
Yep. I agree. The standard deviation is the deviation from the Mean.

2.5 SD's mean is equal to: +/- 2.5*3 = +/- 7.5

ie. 12.5 to 27.5

Answer is: A
Re: PS : Mean & SD   [#permalink] 17 Aug 2010, 11:48
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