Frobisher, a sixteenth-century English explorer, had soil samples from

Question

Frobisher, a sixteenth-century English explorer, had soil samples from Canada’s Kodlunarn Island examined for gold content. Because high gold content was reported, Elizabeth I funded two mining expeditions. Neither expedition found any gold there. Modern analysis of the island’s soil indicates a very low gold content. Thus the methods used to determine the gold content of Frobisher’s samples must have been inaccurate.

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

(A) The gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century.

(B) The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn Island.

(C) The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.

(D) Frobisher did not have soil samples from any other Canadian island examined for gold content.

(E) Gold was not added to the soil samples collected by Frobisher before the samples were examined.

GMATPrep Code  :  VCR005704

KarishmaB · Accepted Answer

Let us read the question stem first. We are looking for an assumption. An assumption is a necessary missing premise. We are looking for the option that needs to be true for the conclusion to be true.

Premises:
Frobisher had soil samples from Canada’s Kodlunarn Island examined for gold content. 
Because high gold content was reported, Elizabeth I funded two mining expeditions. 
Neither expedition found any gold there. 
Modern analysis of the island’s soil indicates a very low gold content.

Tell me, when you read the above premises, what possibilities come to mind? Frobisher had samples examined. High gold content was reported. No gold was actually found. Modern analysis show very low gold content.

The following possibilities come to my mind:
1. Either there was gold and before the expeditions were sent, it was mined (very unlikely!)
2. His methods were inaccurate.
3. Someone had added gold to the soil he tested.

Conclusion:
 The methods used to determine the gold content of Frobisher’s samples must have been inaccurate.

If I am concluding that his methods were inaccurate, then I am assuming that no one added gold to his samples and gold was not mined before the expeditions were sent. (Technically, gold could have been added and his methods could have been inaccurate too but lets not mess with that.)
Hence option (E) is an assumption. 
Also, use you can use assumption negation technique to see that it is the right answer.
I negate (E) : Gold  was added  to the soil samples collected by Frobisher before the samples were examined.

I can not conclude now that his methods were inaccurate.
Hence (E) is the correct answer.

Option (C) is not correct. We did not assume in the argument that his methods were different. They could have been the same ones generally used in the 16th century, It is possible that 16th century methods were not accurate.

buffdaddy · Answer

This is a classic trap in CR. The question asks what is the assumption. An assumption can only lead to the conclusion that is made. The conclusion is that the dude's methods are inaccurate. C talks about the dude was using different methods. If that were the correct assumption, how could one make the conclusion that his methods were inaccurate? The assumption has to solidify the conclusion.

Therefore only E serves this purpose and is correct.

GMATBLACKBELT · Answer

E. This is a very tricky one. (seen this before and had same answer by POE) but looking at it again. E makes a lot of sense. If gold were added then the methods were not inaccurate, but the results were not indicative of the actual content. This is different from accuracy. The methods used could still well have been very accurate in determing the amount of gold (or added gold) there was in the sample. So E is the winner.

zonk · Answer

Premise shows discrepancy b/w Frobisher's soil sample and the two other data points (mining expeditions and modern soil samples). Correct answer must contain an alternate way for Frobisher's soil sample to test positive while explaining the other two data points.

E

chelliyil · Answer

Frobisher could have mistakely examined for gold on any other island as well too. In that case D would be a choice. Please explain why this option is out.

KarishmaB · Answer

The argument says that he got soil from Kodlunarn island examined. The Queen sent two expeditions there. The argument does not have anything to do with the other islands. It does not assume that he did not get soil of any other island examined. Perhaps he did and found no gold there or perhaps he did find gold there. We do not know and do not care as far as this argument goes. Here we are only concerned with Kodlunarn.

nikhilsamuel89 · Answer

Frobisher, a sixteenth-century English explorer, had soil samples from Canada’s Kodlunarn Island examined for gold content. Because high gold content was reported,Elizabeth I funded two mining expeditions. Neither expedition found any gold there. 
Modern analysis of the island’s soil indicates a very low gold content. Thus the methods used to determine the gold content of Frobisher’s samples must have been inaccurate. Which of the following is an assumption on which the argument depends?

Conclusion:  Methods used by  F  to find gold content were inaccurate.

A. The gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century. This says that gold content was high in the 16th century.  Weakens the argument. Hence, cannot be the assumption. 
B. The two mining expeditions funded by Elizabeth I did not mine the same part of Kodlunarn Island.
 Irrelevant. Same part or different part not mentioned anywhere in the stimulus. 
C. The methods used to assess gold content of the soil samples provided by Frobisher were different from those generally used in the sixteenth century.  The difference in methods does not matter. What the conclusion says is the method, in fact, was inaccurate. 
D. Frobisher did not have soil samples from any other Canadian island examined for gold content. Again, irrelevant. 
E. Gold was not added to the soil samples collected by Frobisher before the samples were examined.  Negating, Gold  WAS  added to the soil samples before they were examined. If this were true, then F's methods may have been accurate, and measured HIGH GOLD CONTENT. Hence, the conclusion that F's methods were inaccurate falls apart.

Hope this helps

himanshujovi · Answer

Karishma , can I paraphrase the above highlighted explanation as

Negative E - Gold was added to the soil samples collected by Frobisher before the samples were examined.

Now that if gold was added before examination and the examination rightly pointed this out - it clearly shows that the technical method to determine the gold content was not in-accurate ( though the step of fudging sample was morally wrong but that is altogether a different matter) 
 
So negating assumption , destroys the conclusion , hence E it is

KarishmaB · Answer

Yes, that's correct. If Gold was added, we don't know who did it so we cannot blame Frobisher or his methods. All we know is that his methods to determine gold content could have been accurate.

eiffel · Answer

(A) The gold content of the soil on Kodlunarn Island is much lower today than it was in the sixteenth century.

can someone help me why ( A) is wrong? we assume F's method was correct so, it can possible gold amount today is much lower than sixteenth century.

KarishmaB · Answer

No gold was found in the 16th century either. The soil sent for analysis showed gold. It could have been because it was tampered with or the one analysing the soil messed up etc. 
So we are not assuming that the gold content today is lower. Anyway, the comparison of gold content of today with 16th century has nothing to do with the conclusion. The conclusion is only about 16th century gold content.

zoezhuyan · Answer

Dear experts
 VeritasKarishma ,  GMATNinjaTwo ,  GMATNinja , 
I am struggling with E
if I negate E, then does the argument hurt?

the negation of E is that 
 Gold was  not  added to the soil samples collected by Frobisher before the samples were examined.

if the sample is contaminated, the modern method also tests the contaminated sample,
the modern method show low gold percentage, while the Frobisher's method shows high percentage.
it still can be the Frobisher's method is incorrect. the conclusion is not damaged.

please help. this one does puzzle me a lot.

thanks in advance.

KarishmaB · Answer

The explanation is given here: https://gmatclub.com/forum/frobisher-a- ... ml#p823930 When I say that A happened and it could have happened because of reasons B, C or D, and then I conclude that it MUST HAVE happened because of reason C, I am saying that it did not happen because of B or D. When I conclude that his methods must have been wrong, I am saying that no one added gold to the sample or mined it before the expedition reached. If either one of these cases were true, I would not NEED his methods to be wrong.

zoezhuyan · Answer

dear  VeritasKarishma , thanks for your quick reply.

I can understand your explanation , the link you share with me.

But I have no idea where my reasoning is incorrect, and I am afraid that your reply this time is harder for me.

I geniunely need your further explanation.

thanks in advance.

KarishmaB · Answer

zoezhuyan  -

Modern analyses is conducted on the island's soil, not on the same soil sample that was sent by him for analysis in the 16th century.

We find that the island's soil has no gold but his samples showed high amount of gold. It is possible that someone added gold to the sample at that time.

Now look at our conclusion:
The conclusion is NOT "his methods were wrong". The conclusion is "his methods MUST have been wrong."
We are saying that his methods were necessarily wrong. Now, that is incorrect if gold was added to the soil sample. Then his methods might have been correct. We cannot say that his methods are necessarily wrong. And hence the conclusion cannot hold now.

custodio · Answer

KarishmaB

Does (A) go against the premise?

According to the passage, 
- 16th century, no gold. Say, 0 gram.
- today, very low gold. Say, 10 gram.

According to (A),
- today's gold is lower than 16th century gold.

How it is possible that in today's gold is <0 ?

Thanks.

KarishmaB · Answer

The fact that the mining expedition did not find any gold does not mean that the soil there had no gold at that time. 
High gold content in soil could indicate deposits of gold nearby. Those would be mined. Upon mining, one may or may not find any deposits. It may not be feasible to extract gold from soil (very low percentage). It is possible that soil of many areas will have some gold content - however small it may be (say a few molecules per square metre). 
According to the passage, no gold deposits were found in 16th century. The soil could have higher gold content then than it does now. 
The argument tells us that modern analysis of the soil show very low gold content and hence methods used by Frobisher must have been inaccurate.

Option (A) says that gold content in soil is much lower today than in 16th century. Our argument does not assume this. In fact, it assumes that today there is very low gold in soil so likely there was very low gold at that time too and hence Frobisher's methods were inaccurate. 
Hence, if anything, it assumes that today there is same amount of gold in soil as there was in 16th century. 
That is why (A) is not an assumption.

krndatta · Answer

KarishmaB 
Ma'am, 
Can you share your reasoning for option B? On the look of it, this weakens the conclusion. 
If they did not mine the same part of the island, then his methods may have been accurate.

Please share your two cents

KarishmaB · Answer

Yes, if anything, option (B) weakens the argument. One of the premises for the conclusion is that the two expeditions did not find any gold. If we say that the two expeditions did not mine in the same area, we cannot base our conclusion on the result of the expeditions then. So this support to the conclusion is taken away by option (B) and in this way, our conclusion is weakened. 
Note that in an actual weaken question, we try to look for something that weakens the conclusion directly.

Frobisher, a sixteenth-century English explorer, had soil samples from

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