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m21#26

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Director
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m21#26 [#permalink] New post 12 Dec 2011, 03:57
If the salt concentration in Northern Lake increased by 20% from 1900 to 2000 while that in Southern Lake decreased by 10%, is the current salt concentration in Northern Lake higher than that in Southern Lake?

(1) In 1900 the salt concentration in Southern Lake was 10% higher than that in Northern Lake
(2) In 1900 the salt concentration in Southern Lake was 4%

Can someone please explain why (2) is not sufficient? My reasoning for (2) is like this:
Since the salt concentration in Southern Lake decreased by 10% and from (2) we know that it was 4% in 1900, we can conclude that this concentration was 0 in 2000. Now, even if the concentration in Northern Lake was zero in 1900, we know that it increased by 20%, so it must be greater than zero in 2000. Thus, in 2000 the concentration of salt in NL is greater than in SL.

Please clarify.
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Re: m21#26 [#permalink] New post 12 Dec 2011, 13:13
The question is looking at percentages.

So when it says Southern lake was 4% in 1900 and decreased 10% by 2000, it is asking you to take 10% of 4% (.4%). The new percentage of salt concentration should be 3.6% in the Southern Lake.

I believe the answer should be C.
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Re: m21#26 [#permalink] New post 13 Dec 2011, 02:12
The OA is actually (A).

The question says:

Quote:
decreased by 20%


For example: Quantity of sugar decreased by 10% (of the original quantity). It means that if it were 100%, now it is 90% (of the original quantity).

Quote:
In 1900 the salt concentration in Southern Lake was 4%


4% is of what quantity? Original?

Can someone please explain the question and specifically (2)?

Thanks a lot.
Re: m21#26   [#permalink] 13 Dec 2011, 02:12
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m21#26

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