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# Gmat Prep Standard deviation

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Senior Manager
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Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 01:21
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(N/A)

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0% (00:00) correct 100% (00:00) wrong based on 1 sessions
No idea how to solve this...........
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Intern
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 02:46
I'm not completely sure but I think 6 and 6.

Standard deviation is lower when data points of the set are closer to the mean so if you add two data points which are the same as the mean it should result in a lower SD.
Senior Manager
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 02:46
E

Std. Dev. = sqrt(((a1-mean)^2+(a2-mean)^2....+(an-mean)^2))/n) where an = elements of set.

When we add 2 elements to the set which are exactly the same as mean. We do not change the nominator of the formula and we increase the denominator. Thus, we decrease the std. dev.
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 04:57
fiercepoint wrote:
I'm not completely sure but I think 6 and 6.

Standard deviation is lower when data points of the set are closer to the mean so if you add two data points which are the same as the mean it should result in a lower SD.

I got what u are trying to say.....thanks the OA is E
Senior Manager
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 04:58
maliyeci wrote:
E

Std. Dev. = sqrt(((a1-mean)^2+(a2-mean)^2....+(an-mean)^2))/n) where an = elements of set.

When we add 2 elements to the set which are exactly the same as mean. We do not change the nominator of the formula and we increase the denominator. Thus, we decrease the std. dev.

Thanks... the OA is E
Director
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 05:30
I wouldn't even worry about formula of standard deviation. Standard deviation is a measure of deviation from the mean. If you add datapoints that are very close to the mean, standard deviation decreases. If you add datapoints that are far away from the mean, standard deviation increases.
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 10:36
IMO E , avg/mean is 6, standard deviation is displacement from avg/mean , to reduce the standard deviation, the most appropriate value is avg itself.. hope i did it right.
Senior Manager
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Re: Gmat Prep Standard deviation [#permalink]  29 Sep 2009, 20:32
Thanks guyzz you all are perfectly right...
Re: Gmat Prep Standard deviation   [#permalink] 29 Sep 2009, 20:32
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