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# A certain list of 100 data has an avarage (arithmetic mean)

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Current Student
Joined: 05 Feb 2008
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A certain list of 100 data has an avarage (arithmetic mean) [#permalink]

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22 Mar 2008, 04:58
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

A certain list of 100 data has an avarage (arithmetic mean) of 6 and a standard deviation of d, where d is positive. Which of the following pairs of data, when added to the list, must result in a list of 102 data with standard deviation less then d?

1. -6 and 0
2. 0 and 0
3. 0 and 6
4. 0 and 12
5. 6 and 6

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Director
Joined: 10 Sep 2007
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22 Mar 2008, 06:50

SD is measure of deviation of data from mean/average. Given that average is 6. Also given that D is +ve, means there is some sort of deviation.

If you add values, which are same as mean/average that will lower the deviation (because you are adding two more values to the series which are contributing to zero deviation, which means you are adding 2 values in series without increasing deviation thereby deviation will decrease).

As 6, and 6 is same as mean/average, so they will lower the deviation.

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Senior Manager
Joined: 15 Aug 2007
Posts: 252

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22 Mar 2008, 07:47
E - deviation is minimum (zero) for these values.

Try this -> http://davidmlane.com/hyperstat/A16252.html (you don't the material on second page for GMAT).

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Current Student
Joined: 05 Feb 2008
Posts: 54

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22 Mar 2008, 08:59
OA is E.
Thanks for the explanations.

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Re: Standard deviation   [#permalink] 22 Mar 2008, 08:59
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