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GMATPrep Question on SD

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GMATPrep Question on SD [#permalink] New post 19 Aug 2006, 02:06
Please solve this GMATPrep Question : kindly ignore the answer choice marked in the screen shot.
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shinewine

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 [#permalink] New post 19 Aug 2006, 05:30
Answer A.

same amount is removed from each tank and so the Standard deviation remains same after this remove.

A says SD still same.


B talks about average of 6 tanks 63. Not sufficient.
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 [#permalink] New post 19 Aug 2006, 22:17
baski6 wrote:
Answer A.

same amount is removed from each tank and so the Standard deviation remains same after this remove.

A says SD still same.


B talks about average of 6 tanks 63. Not sufficient.


I am really bad.. at SD.. can you please elaborate the answer...
also can you please guide me ..how can i improve on the concepts..of SD
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 [#permalink] New post 19 Aug 2006, 22:25
A

SD is measure of the variations of the elements of set with respect to mean.

Lets say water tanks have
10 , 20 , 30, 40, 50 , 60 gallons
Now after removing 30% from each we have
7,14,21,28,35,42

As all elements are reduced by 30%, the mean will also be reduced by 30%. So the variation of elements with respect to the new mean is also same. So SD will remain the same.

statement 2 don't tell the scenario after the removal. So its INSUFF.
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 [#permalink] New post 19 Aug 2006, 23:09
ps_dahiya wrote:
A

SD is measure of the variations of the elements of set with respect to mean.

Lets say water tanks have
10 , 20 , 30, 40, 50 , 60 gallons
Now after removing 30% from each we have
7,14,21,28,35,42

As all elements are reduced by 30%, the mean will also be reduced by 30%. So the variation of elements with respect to the new mean is also same. So SD will remain the same.

statement 2 don't tell the scenario after the removal. So its INSUFF.



Thank you.. now i get it.. i wasted some 5 minute on this problm.. while doing the GMATPrep test..
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  [#permalink] 19 Aug 2006, 23:09
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