OA: A

Although, I was able to solve this, but still I am inviting experts to provide their perspective.

I believe that Option C and Option E are very similar to each other. Therefore they both should be discarded. Thanks!

richachampion wrote:I believe that Option C and Option E are very similar to each other. Therefore they both should be discarded. Thanks!

They're not exactly the same.

C negated: There are not salts that leach into the Earth's oceans directly from the ocean floor.
It doesn't matter if salt comes from sources other than rivers. What we care about is the overall rate at which the salt is increasing. Because the negation of C is irrelevant, it's wrong.

E negated: Some of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans.
This doesn't undermine the conclusion. It's possible that "some" refers to a negligible amount of salt. So long as the salt is increasing at the same rate over many centuries, we'd still be able to estimate the ocean's age. E is out.

DavidG@VeritasPrep wrote:They're not exactly the same.

Actually, sir, they are the one and the same in one respect. I am not a native speaker so my expression power is not that good, but still, I will try to explain what I mean.

C. There are salts that leach into the Earth's oceans directly from the ocean floor.
E. None of the salts carried into the Earth's oceans by rivers are used up by biological activity in the oceans

We are relying on the net increase/century.
Salts ± Other Sources = resulting increase
Notice I have used both "+" and "-" signs because other sources may add or subtract to the salt added by rivers, but remember that we are concerned about net increase.
This is not an assumption you can test it by negating this option, and it will never break the conclusion.

I am giving you an analogous example suppose there is a boy by a name of Gajat Rugnani and his mother gives him money to deposit

+VE Example: Gajat Rugnani is a nice boy and he works hard and earn 10$ every month andd that to the 100$ given by his mother and he deposit every month 110$, so when he has 11000$ and we know that he deposits 110$/month we can safely calculate w/o any error that he has been depositing since 100 months

-VE Example: Gajat Rugnani is a dishonest and naughty boy 100$ every month and he is dishonest and he spends 10$, but deposit only 90$ in his Piggy Bank. So based on a constant depoist every month if we have 9000$ in his Piggy bank we can safley calculate that he has deposited for 100 months despite 10$ was reduced every month, but still it didnt cause erropr in calculating how many months since he is depositing.

Now irrespective of whether Gajat Rugnani is hardworking or dishonest or none, and thus irrespective of whether
Gajat Rugnani deposits 90$, 100$, or 110$ based on the resultant we can safley calculate the total # of months of his deposit.

Thus in our main option too resultant deposit matters and as such it is not a unstated assumption because assumption is something w/o which conclusion/argument can't stand.

Let me add little , as per reasoning author states that one can extrapolate last 100 years data till end to calculate the ocean's age. so assumption should be that extrapolation(linear) is possible and no randomness between centuries.

A addresses this well, where as in E ,apart from extreme word, biological activity can also be extrapolated to all previous centuries . Since its doesn't convey randomness between centuries.

Hope it makes sense.

DavidG@VeritasPrep sir, Did you get my point. The two options are literally not same not rephrased, but logically they are same with same effect and 2 answers can't be true and thus can be discarded. I have seen this pattern in many GMAC problems.

richachampion wrote:DavidG@VeritasPrep sir, Did you get my point. The two options are literally not same not rephrased, but logically they are same with same effect and 2 answers can't be true and thus can be discarded. I have seen this pattern in many GMAC problems.

Well, if your point is that the answer choices are similar in the sense that neither qualifies as a necessary assumption because neither addresses the issue of the rate of change over time, that's fair enough. Thinking about it more broadly, I'd say the reasonable lessons to draw from this question are as follows:

1) If an answer choice is irrelevant to the conclusion, it's wrong
2) If two answer choices convey the same information, they must both be wrong

We're on the same page here. But I'll add one more.

3) If two answer choices feel similar, but there could be some reasonable disagreement about whether they're identical, consider each option's impact on the conclusion separately just to be safe.