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standard deviation

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Junior | Next Rank: 30 Posts
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by gte793n » Tue Sep 04, 2007 5:26 pm
standard deviation always gets me...

If a certain sample of data has a mean of 20.0 and a standard deviation of 3.0, which of the following values is more than 2.5 standard deviations from the mean?

a) 12.0
b) 13.5
c) 17.0
d) 23.5
e) 26.5



the answer: A

I have no idea what the question is asking..

source: OG

Thank you in advance.. :)
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Master | Next Rank: 500 Posts
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Joined: Tue Aug 07, 2007 1:45 amFollowed by: 1 member

by agps » Wed Sep 05, 2007 2:59 am
mean = 20
deviation =3

more than 2.5 deviations from mean (3*2.5 = 7.5, because 1 deviation is 3) any number farther than 7.5 from 20

only possible answer is A.
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Master | Next Rank: 500 Posts
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by ri2007 » Wed Sep 05, 2007 3:27 pm
Hey gte793n

Standard Deviation is really a simple concept

Think of the mean as the centre. SD is the distance from the mean.

Stastically it just denotes the normal deviation or the variation of the values from the mean or the centre value.

Hope this helps!!!
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Junior | Next Rank: 30 Posts
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Joined: Wed Jul 25, 2007 10:48 am

by gte793n » Wed Sep 05, 2007 4:56 pm
thanks for your help guys!
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