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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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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.
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?
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?
abhijit.. it happens ... GMAT was made to make fools out of us....
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. 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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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.
Originally posted by Nerdboy on 04 Sep 2008, 04:00.
Last edited by Nerdboy on 05 Sep 2008, 00:31, edited 1 time in total.
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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?
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
. 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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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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