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The Earth s rivers constantly carry dissolved salts into its

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Re: CR Salt content [#permalink] New post 13 Oct 2010, 19:24
Has to be A. At no point does the argument make any assumptions about the river's salt content being the same. Since rivers dump into the ocean their salinity can be different. It does make the assumption that at one point the ocean had a salt free base that was likely equal to the rivers, but this is not what B says. So it has to be A.
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Re: CR Salt content [#permalink] New post 14 Oct 2010, 09:25
E
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Re: CR Salt content [#permalink] New post 15 Oct 2010, 04:25
I chose E. CRs are killing me
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Re: CR Salt content [#permalink] New post 07 Oct 2011, 04:35
A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

Between A and E.
1. Averages get skewed if there is unusual variations. The argument assumes there are NONE.
2. Try and negate this --> NOT ALL of the salts carried into the Earth's oceans by rivers are used by biological activity in the oceans. Now it becomes clear that this sentence is harmless to the argument.

The problem here lies in the negation process. We have to be careful not to go for POLAR opposites during negation. If we go for POLAR opposites the answer becomes " ALL of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans."
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Re: CR Salt content [#permalink] New post 07 Oct 2011, 06:59
Nice question. Narrowed it down to A and E. But chose E, without further thoughts. Got it wrong :(

A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

Loved the explanation that we can account the factor of consumption of salt but not for unusually large amount of deposits of salt for which we have no data.
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CR notes
http://gmatclub.com/forum/massive-collection-of-verbal-questions-sc-rc-and-cr-106195.html#p832142
http://gmatclub.com/forum/1001-ds-questions-file-106193.html#p832133
http://gmatclub.com/forum/gmat-prep-critical-reasoning-collection-106783.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html?hilit=chineseburned

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Re: CR Salt content [#permalink] New post 07 Oct 2011, 14:38
A is the answer...
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Re: CR Salt content [#permalink] New post 09 Oct 2011, 18:47
i am also with E
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Re: CR Salt content [#permalink] New post 10 Oct 2011, 22:18
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hibloom wrote:
The Earth’s rivers constantly carry dissolved salts into its oceans. Clearly, therefore, by taking the resulting increase in salt levels in the oceans over the past hundred years and then determining how many centuries of such increases it would have taken the oceans to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth’s oceans can be accurately estimated.

Which of the following is an assumption on which the argument depends?

(A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
(B) At any given time, all the Earth’s rivers have about the same salt levels.
(C) There are salts that leach into the Earth’s oceans directly from the ocean floor.
(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.


The method is purely based on the observations from the past 100 years, so we need to something which points out the flaw in this method.

(A) The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. CORRECT. this says the rate of salt deposited in the last 100 years is unusually high. This clearly weakens the argument.
(B) At any given time, all the Earth’s rivers have about the same salt levels. irrelevant
(C) There are salts that leach into the Earth’s oceans directly from the ocean floor. if salt leaches into the oceans directly, it would have done so in the past 100 years as well. so it doesnt point to a flaw in the proposed method.
(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
Ignore it
(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
if oceans use salt for biological activities. it would have done so in the past 100 years as well. so it doesnt point to a flaw in the proposed method
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Re: CR Salt content [#permalink] New post 12 Oct 2011, 05:54
IMO A.
It was clearly between A and E.

Here is what I thought:

The key word here is "increase". The questions clearly says that the age can be calculated based on the "increase" in salt level. Hence, as long as the salt lost due to biological activity is constant, it does not make any difference to the process defined.
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Re: CR Salt content [#permalink] New post 12 Oct 2011, 07:25
thanks for this!
durgesh79 wrote:
between A and E...
one of the best ways for CR assumption questions
negate the assumption and the argument should fall apart.

negate E
Some of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
OK.. but if the portion of salt consumed by biological activities has remained constant over the years ... we can still predict the age of the oceans ... the argument doesnt fall apart

negate A
The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years.
it means that the rate has not been constant .... we cant predict the age .... agrument falls apart ...

right Option A

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Re: CR Salt content [#permalink] New post 12 Oct 2011, 16:58
A
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Re: CR Salt content [#permalink] New post 21 Oct 2011, 12:25
+1 A
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Re: CR Salt content [#permalink] New post 21 Oct 2011, 18:37
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A tough one and after much deliberation I choose option A.

To simplify this lets consider that I can walk at a constant rate of 10 km/hr. On a given day I walk 20 kms. It took me 2 hours to cover the distance. The result (time to cover the distance) is depending on the walking rate and not the distance I covered. If I start walking at a higher rate it will take me less time to cover the distance.

Similarly the age of the ocean = Increase in salt level/rate of deposition per century. The assumption is that the rate of deposition is constant; otherwise the result will be inaccurate.

Option A: The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years. –this means that the rate of deposition is constant and thus we can accurately calculate the age of the ocean.

Using method of negation
Option E – All (polar opposite of none) of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans. – extreme assumption. Moreover it doesn’t weaken the conclusion as we can still calculate the age of the ocean.

Option A - The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years. – the rate of deposition is not constant. The conclusion falls apart. We can’t accurately calculate the age of the ocean
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Re: CR Salt content [#permalink] New post 01 Nov 2011, 22:40
+1 A
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 16 Nov 2011, 22:28
Between E and A but E fails the negation test so A it is.
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 16 Nov 2011, 23:59
Still not satisfied with A,


can anyone clearly explain why not E and why A?

Thanks in advance
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 17 Nov 2011, 00:29
A tricky one to choose between A and E ! I agree with the explanation of A . But could someone explain a bit more why E is not that much convincing like A?

Thanks
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 17 Nov 2011, 02:02
Got it wrong. Opted for B
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 21 Nov 2011, 01:18
imo A
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Re: The Earth s rivers constantly carry dissolved salts into its [#permalink] New post 21 Nov 2011, 04:09
IMO E,

OA -A cannot be correct.The conclusion is that from the deposited salt the oceans age can be calculated.However, if the salt is used up then the age cannot be accurately calculated.

Hnece E is the perfect assumption.
Re: The Earth s rivers constantly carry dissolved salts into its   [#permalink] 21 Nov 2011, 04:09
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