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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]

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New post 04 Sep 2008, 03:37
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

. 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.

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Re: S.D of consecutive nos. [#permalink]

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New post 04 Sep 2008, 03:47
I will go with D.

Since, the numbers are consecutive even numbers, average or median will remain the same only if the two extreme numbers are removed. And, hence, it will be possible to calculate the SD.

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Re: S.D of consecutive nos. [#permalink]

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New post 04 Sep 2008, 04:00
I think E.

We have from the stem that the average is the same as the median and it is 11. We can remove two numbers without changing the median/average, by removing any of the pairs: 2&20, 4&18, 6&16, 8&14, 10&12. I never bothered to remember how stdev is calculated, but if we remove 2 and 20, it will be different than removing 10 and 12, right?
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Last edited by Nerdboy on 05 Sep 2008, 00:31, edited 1 time in total.

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Re: S.D of consecutive nos. [#permalink]

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New post 04 Sep 2008, 04:59
If you remove 4 and 18 or 6 and 16, the average will change.

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New post 04 Sep 2008, 05:00
Oops....my silly mistake.....it will be E.

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Re: S.D of consecutive nos. [#permalink]

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New post 04 Sep 2008, 09:01
Even though average/median remains the same, the SD for a subset of the numbers will be different because the numerators (in calculation of SD) varies. Hence E

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Re: S.D of consecutive nos. [#permalink]

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New post 05 Sep 2008, 22:19
arjtryarjtry wrote:
. 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.

When we symmetrically remove the data the mean and median remain unchanged but SD is distance from the mean hence which values removed does matter here !!!Hence in both the options cant say!!
IMO E
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Re: S.D of consecutive nos.   [#permalink] 05 Sep 2008, 22:19
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