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If two numbers are removed from 2, 4, 6, 8, 10, 12, 14, 16,

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If two numbers are removed from 2, 4, 6, 8, 10, 12, 14, 16, [#permalink] New post 28 Jul 2008, 18:58
If two numbers are removed from 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20, what is the standard deviation of the remaining numbers?
(1) The average remains unchanged after the numbers removing.
(2) The median remains unchanged after the numbers removing.

A. Statement (1) ALONE is sufficient but Statement (2) ALONE is not sufficient.
B. Statement (2) ALONE is sufficient but Statement (1) ALONE is not sufficient.
C. BOTH Statements TOGETHER are sufficient, but NEITHER Statement alone is sufficient.
D. Each Statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.
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Re: avg , and MEDIAN [#permalink] New post 28 Jul 2008, 19:08
For ordered series median and mean is always same.
Since the given series is an ordered series, so statement 1 and 2 are essentially telling us same thing.
These statements implies that numbers removed are equidistant from average. One of left hand side and the other on right hand side. Removing such numbers is not going to affect the std. deviation.

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Re: avg , and MEDIAN [#permalink] New post 28 Jul 2008, 19:13
i think it is E.
for same avg/ median, we ahve to remove nos symetrical about the median nos.
so if we remove 6 and 16, we get a diff SD than when we remove ,say 4 and 18.
is logic ok?
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Re: avg , and MEDIAN [#permalink] New post 28 Jul 2008, 19:16
arjtryarjtry wrote:
i think it is E.
for same avg/ median, we ahve to remove nos symetrical about the median nos.
so if we remove 6 and 16, we get a diff SD than when we remove ,say 4 and 18.
is logic ok?

Sorry I messed up with idea, you are right.
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Re: avg , and MEDIAN [#permalink] New post 28 Jul 2008, 19:23
abhijit.. it happens ... GMAT was made to make fools out of us.... :lol:
Re: avg , and MEDIAN   [#permalink] 28 Jul 2008, 19:23
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