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# The Earth's rivers constantly carry dissolved salts into its oceans.

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The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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06 Jan 2008, 17:04
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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 ocean to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth's oceans can be accurately estimate.

Which of the following is the 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.
[Reveal] Spoiler: OA
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 22:23
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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: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 19:37
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priyankur_saha@ml.com wrote:
IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result

If the quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years , it will surely affect the result.

Consider the salts deposited in the past century is X.

The current salt level is say 5X

so as per the result ocean's age is 5 centuries.

But if X is unusually large and the deposited salt level of previous centuries were say only X/4 per century then the result will have a blunder!
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 18:17
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Conclusion: the maximum age of the Earth’s oceans = (Current Salt Level - hypothetical initial salt-free state) / (the oceans over the past hundred years)

Assumption: For every year there is constant salt deposit in the ocean. If not, this argument falls apart.

B
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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06 Jan 2008, 19:02
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Expert's post
ttram wrote:
msday86 wrote:
I think the assumption is that the increase in salt level is constant throughout time. So, I think A is the answer. If the increase in level over the last 100 years in unusually high, then that invalidates the method.

I agree with you that A is right. However, what do you think about E?

After re-reading choice E several times (which I may not have done on the real GMAT), it seems to be irrelevant.
The argument says to take the difference between salt levels today and 100 years ago and then divide the total salt level by the difference. Choice E says that there may be some biological activities using up the salts, which is fine since these biological activities have been active longer than 100 years, so they are a constant. Every 100 years these biological activities consumed the same amount of salt. Surprisingly, choice E can be ruled out mathematically.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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19 Jun 2008, 13:59
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lexis 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.

Consider A,
A. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.

Negate it ->

The quantities of dissolved salts deposited by rivers in the Earth’s oceans have been unusually large during the past hundred years.

Clearly then our experiment to determine age of the oceans will fail.
So, this is an assumption the argument relies upon.

IMO - A
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 07:06
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IMO E.
* The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
Deposit could be large but that never hampers the result
* At any given time, all the Earth’s rivers have about the same salt levels.
OOS
* There are salts that leach into the Earth’s oceans directly from the ocean floor.
OOS
* There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
OOS
* None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
If biological process uses the same salt, concentration will definitely fall
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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05 Oct 2010, 08:29
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hibloom wrote:
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.

i was a difficult choice between a and e.
I eliminated E with the foll. reasoning.
If at the beginning of the last century,the ocean contained x kgs of salt.
If in the last 100 years , 100 kgs of ice was dropped into the ocean by the rivers.
and suppose that in the past 100 yrs 5 kgs of salt was used up by the ocean because of its biological activity.
then 95 kgs was dropped in the last century.
So the level becomes x + 95
still we can find out the age of the ocean by taking 95 kgs as the average increase in 1 century.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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05 Oct 2010, 19:24
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I initially had a strong urge to choose E after I narrowed down A and E.

However after some time thought option E could be broken but not A. Here is why:

Option E talks about "none of the salt getting used up". By taking the resulting increase in salt levels in the oceans over the past hundred years we could accommodate the the condition wherein some of the salt is being used up.

Hence option E is not the safe assumption to make. Hence A is the answer.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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05 Oct 2010, 20:10
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Has to be A as biological activity will happen every year.

So if rivers bring salt S and biological consumption is s then for a year the Salt increase would be S-s.
So even if we look at a long period every year s amount of salt gets consumed by biological consumption.
That way we can calculate the no of years based on X/(S-s) where X is total increase in the Salt content. So biological activity should not be a problem.

Thanks
Arun
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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10 Oct 2011, 23:18
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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: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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21 Oct 2011, 19:37
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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: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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26 Jan 2013, 02:01
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Level of salt in the ocean = could be use to predict the age of oceans...
How? determining the number of centuries it took to reach current salt-level from less-salt state...

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.
If salt level in the past was also unusually large as now, then perhaps there is no such thing as increase in salt levels that could help determine the age...

(B) At any given time, all the Earth’s rivers have about the same salt levels.
Rivers can have different salt levels and the conclusion will still hold... This is not assumed...

(C) There are salts that leach into the Earth’s oceans directly from the ocean floor.
If there are salts from the ocean floor and salts from river, the comparison of the levels of salt today and past hundred years will still work as an age determinant... TThe conclusion will still hold...

(D) There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans.
Extreme... There's no claim about the superiority of these method compared to other methods...

(E) None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.
Even if salts are used up by the oceans, as long as that consumption rate is the same althroughout.. the method will still work.. This trap is similar to (C) in that it introduces factors other than rivers to contribute to change in salt levels... (e.g. Ocean floor and Biological Process) as long as the salt levels did increase from past to now... then the method will work...

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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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09 Jan 2008, 12:33
ttram 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 ocean to reach current salt levels from a hypothetical initial salt-free state, the maximum age of the Earth's oceans can be accurately estimate.

Which of the following is the 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.

We can eliminate B, C and D after reading.
The argument is talking about: We can guess the maximum Earth's age when we calculate dissolved salts from rivers to oceans with the premise is at the first time, the salt level of oceans is zero.

B: Irrelevant because we do not discuss about salt level in rivers. It does not lead us to the conclusion.
C: Irrelevant, too.
D: Although it seems to be a right answer because it talks about a method. However, it is too general, and not assume anything.
E: The first time, I think E is the best answer. However, it is a mistake. First, it is too specific. If none of the salts were used by biological activity, so, how about other activities? (such as physical activity, chemical activity...)? Second, it does not lead us to a conclusion. We cannot conclude that the method is accurate because of the premise E.
A: It supports the premise:
Premise:
- At the first time, the salt level of oceans is zero.
- We calculate the salt level of oceans in the past hundred years, and we can know the Earth's age.
- In a process, the quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.
- Thus, we can convince that the result is believable.

I hope that you guys can accept my explanation.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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19 Jun 2008, 13:11
lexis 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. - So....?
B. At any given time, all the Earth’s rivers have about the same salt levels. - Not a required assumption
C. There are salts that leach into the Earth’s oceans directly from the ocean floor. - Weakens
D. There is no method superior to that based on salt levels for estimating the maximum age of the Earth’s oceans. - We dont care
E. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

E.
The assumption is that whatever is carried stays and none is used and hence the correlation can be drawn using the method described. Negate this assumption and we are left with decreasing amounts of salt and hence no correlation can be accurately undertaken.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 12:33
hey alpha y dont you share your line of reasoning
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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15 Aug 2008, 19:24
Only B & E makes sense

B : only if the salt content carried by the river is constant, will the calculation of salt content in the ocean be possible.

E : this seems to more directly implied than the previous one.

Hence I would go with E

Whats the OA??
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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05 Oct 2010, 22:30
C and D are out .
From A, B and E
I chose E.
For A-it is not about large quantities or small quantities.
For B-We are concerned about the total salt content of all rivers to be same not independent rivers.
For E-it is a perfect answer.
Furthermore if you negate E.conclusion weakens that we may not get the true age.

Please let me know if i am correct
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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20 Jul 2011, 22:07
My original prediction before seeing the answers was that the rate by which salt was deposited in the last century must be representative of the centuries since the dawn of Earth.

But, since I'm still a careless noob at this point, I broke from my strategy and chose E.

Quote:
E. None of the salts carried into the Earth’s oceans by rivers are used up by biological activity in the oceans.

Remember, though, that we're looking only for an accurate estimate. So we don't need to be so bold (well, extreme) and assume none of the salts are used up by biological activity. They can. This is an estimate after all, right?

Quote:
A. The quantities of dissolved salts deposited by rivers in the Earth’s oceans have not been unusually large during the past hundred years.

Reading A again, I should have stuck with my prediction. For this argument, we must assume that the salt deposited wasn't unusually large during the last century. Else, we'd undershoot the age of the Earth -- certainly more than by a variance in our estimate of age due to biological activity. A is the correct answer IMO.
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Re: The Earth's rivers constantly carry dissolved salts into its oceans. [#permalink]

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07 Oct 2011, 05:35
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."
Re: The Earth's rivers constantly carry dissolved salts into its oceans.   [#permalink] 07 Oct 2011, 05:35

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