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A certain list of 100 data has an avarage (arithmetic mean) [#permalink]
22 Mar 2008, 03:58
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
Can someone point me where I can learn more about standard deviation?
Re: Standard deviation [#permalink]
22 Mar 2008, 05:50
I think answer is E.
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.