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# Standard deviation - PS - GMAT Prrep

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Director
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Standard deviation - PS - GMAT Prrep [#permalink]  06 Nov 2006, 08:05
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How to solve this ..?
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Manager
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No solving - standard deviation is invariant to adding a constant. Try proving it. It's very easy proof.
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Re: Standard deviation - PS - GMAT Prrep [#permalink]  06 Nov 2006, 10:29
mean for new set of values = m+5.....if m istrhe mean for x,y and z...'

sd= ((x+5) - (m+5))^2+......= d

aans is d..choice a
Manager
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Yeah standard deviation will not change....if you want to know the reasoning behind it look up how to solve for a standard deviation and then plug in some numbers. It then becomes clear why adding a constant does not change the SD but multiplting it by something can.
Manager
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I just picked simple numbers for x y z, such as 1 2 3

Add 5 to each, same Std Dev.

A) d
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Right.. adding a constant no to all three wouldn't change the standard deviation.
Director
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Got it .. Thanks everyone ..
Got a very imp concept cleared ..

Regds,
Amit
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