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Standard Deviation

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Manager
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Standard Deviation [#permalink] New post 16 Jan 2010, 02:04
Hi,
Can anybody look into this problem and explain the reasoning behind:

Which of the following sets has the same standard deviation as set (a.b,c)?
a) (ab,b^2,cb)
b) (2a,b+a,c+b)
c) (0,b+a,c-a)
d) (ab,bc,ac)
e) (ab+c,a(1+b),b(1+a))
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Re: Standard Deviation [#permalink] New post 16 Jan 2010, 05:17
Answer is E

(ab+c,a(1+b),b(1+a))

=(ab+c,a+ab,b+ab)

For all the three terms ab is added equally.

Since standard deviation is a measure of the spread of a set of values from the mean value.The spread of (ab+c,a+ab,b+ab) is equal to spread of set (a,b,c).

One can better explain this by taking example values
a=1,b=2,c=3

Sd is same for (1,2,3) and (5,3,4)

Hope this helps :-D
Manager
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Re: Standard Deviation [#permalink] New post 16 Jan 2010, 10:01
Thanks for the nice explanation.
Re: Standard Deviation   [#permalink] 16 Jan 2010, 10:01
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