Standard Deviation Question

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spucmu: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Sat Nov 07, 2009 8:03 pm

by spucmu » Sat Apr 30, 2011 12:57 pm

For the attached question:

Shouldn't the answer be E?

One evenly spaced set can be:

2,4,6

Another can be
4,6,8

Both have deviation of 2 around mean but second set has higher range.

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Source: Beat The GMAT — Data Sufficiency | Sat Apr 30, 2011 12:57 pm

parkman: Senior | Next Rank: 100 Posts; Posts: 31; Joined: Thu Apr 14, 2011 12:37 pm; Thanked: 1 times

by parkman » Sat Apr 30, 2011 1:35 pm

The Range in your two examples is the same.

in a set of 2,4,6

Range = 6-2 = 4

in a set of 4,6,8

Range = 8-4 = 4

So the SD will be the same with the same number of terms and even spacing

If set A has a greater range

{0,5,10)

SD = 5

If set B has a smaller range

{1,2,3}

SD = 1

So answer is C

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spucmu: Junior | Next Rank: 30 Posts; Posts: 17; Joined: Sat Nov 07, 2009 8:03 pm

by spucmu » Sat Apr 30, 2011 3:58 pm

Right, can't believe I am making such dumb mistakes.

Point is that:
If two sets are evenly spaced and one has greater range than another then the set which has the greater range has standard deviation provided number of elements are same.

Thanks!

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