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Source: Beat The GMAT — Data Sufficiency |
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richardwang6430
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HarvardDreamin
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Interesting question - What is the right answer?mleviko wrote:I would go for [A], what is the OA?
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simplyjat
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In my opinion the answer should be E.
Standard Deviation remains same if the same amount is added/subtracted, from each individual. So we know that same amount is added/subtracted from each individual the standard deviation did not change.
The conversion between average and standard deviation, and vice versa, is impossible, if there individual items are missing...
A tells us that same percentage was removed from each tank, but says nothing about the actual amount and thus insufficient.
Standard Deviation remains same if the same amount is added/subtracted, from each individual. So we know that same amount is added/subtracted from each individual the standard deviation did not change.
The conversion between average and standard deviation, and vice versa, is impossible, if there individual items are missing...
A tells us that same percentage was removed from each tank, but says nothing about the actual amount and thus insufficient.
simplyjat
Well, if you substract from each individual the same proportionate amount, the standard devation from the average remains the same. And because we're told the exact std we can answer the question with statement (1).
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simplyjat
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Well did some simple calculations and it turns out that there is a direct relation between the individual items and standard deviation.
When all the elements are increased/decreased by same percentage, standard deviation also increases/decreases by the same percentage
So in the question, the standard deviation will also decrease by 30% and become 7
When all the elements are increased/decreased by same percentage, standard deviation also increases/decreases by the same percentage
So in the question, the standard deviation will also decrease by 30% and become 7
simplyjat
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Stuart@KaplanGMAT
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Close! If it's a proportionate amount, the SD will change proportionally.mleviko wrote:Well, if you substract from each individual the same proportionate amount, the standard devation from the average remains the same. And because we're told the exact std we can answer the question with statement (1).
If we subtract the same amount from each individual term, then SD remains the same.
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