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# GMATPrep Question on SD

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Manager
Joined: 28 Jan 2006
Posts: 116

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19 Aug 2006, 03:06
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Please solve this GMATPrep Question : kindly ignore the answer choice marked in the screen shot.
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shinewine

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Director
Joined: 17 Jul 2006
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19 Aug 2006, 06:30

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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Manager
Joined: 28 Jan 2006
Posts: 116

Kudos [?]: 63 [0], given: 0

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19 Aug 2006, 23:17

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.

also can you please guide me ..how can i improve on the concepts..of SD
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shinewine

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CEO
Joined: 20 Nov 2005
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Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

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19 Aug 2006, 23:25
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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SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

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Manager
Joined: 28 Jan 2006
Posts: 116

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20 Aug 2006, 00:09
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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shinewine

Kudos [?]: 63 [0], given: 0

20 Aug 2006, 00:09
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