Two experimental garden plots were each planted with the same number o

E.

1st premise: The pot with Magnesium salts produced a higher yield.
2nd premise: nothing but water was added to the soil.
The conlusion: Magnesium salt must be responsible for the higher yield.

The key here is "must be." E undermines the conlusion becuase it introduces factors other than magnesium salts that could be reponsible for the higher yield. If the soil texture and sunlight exposure are different, they may have caused the yield to be different and undermine the conclusion that Magnesium salt was the sole cause.

I agree that the answer is E.

I want to offer what I see as the distinction between D and E.

In D, the answer appears to offer an alternative explanation for the difference in production of crops. In stating that weeds were the cause, the answer also states that the reason the weeds could not compete in plot 1 was due to the salts in Plot 1 and not in Plot 2. This is still a cause and effect where the salts are the cause. It adds in an extra step....1) Salts prevent weeds from growing 2) lack of weeds allows crops to produce more CONCLUDE that salts helped in producing more tomatoes.

In E, the answer offers alternatives completely separate from the salts in Plot 1. There is no connection between the reason offered in E and the salts, but in D there is a connection to the reason offered (weeds) and the salts.

So E is the answer, and D seems close, but still supports the connection of salts to production.

I think D is a trap answer. It actually supports the argument.

The premise actually says mag salt increased yield, it doesn't say mag salt caused the tomato plant to produce more. So whether the salt increased yield because it was conductive for the growth of tomato or damaging to the growth of weeds, which is detrimental to tomato, is not relevant.
choice D states that mag salt helped kill the weeds, leading to higher yield, Which is precisely the original conclusion that we seek to weaken--mag salt leads to higher yield.

agree with clear E.
The conclusion of the stimulus is that 'the higher yields in the first plot must have been due to the magnesium salts.'
Cause( magnesium) - Effect(higher yields)
E is saying magnesium is not a cause of higher yields, reveals other reasons such as soil texture and exposure to sunlight. So it weakens the conclusion.

Yes, E is the answer.

I like this question, it did not make me go dizzy as many others do.

Two experimental garden plots were each planted with the same number of tomato plants. Magnesium salts were added to the first plot but not to the second. The first plot produced 20 pounds of tomatoes and the second plot produced 10 pounds. Since nothing else but water was added to either plot, the higher yields in the first plot must have been due to the magnesium salts.
Which of the following, if true, most seriously weakens the argument above?

(A) A small amount of the magnesium salts from the first plot leached into the second plot.
(B) Tomato plants in a third experimental plot, to which a high-nitrogen fertilizer was added, but no magnesium salts, produced 15 pounds of tomatoes.
(C) Four different types of tomatoes were grown in equal proportions in each of the plots.
(D) Some weeds that compete with tomatoes cannot tolerate high amounts of magnesium salts in the soil.
(E) The two experimental plots differed from each other with respect to soil texture and exposure to sunlight.

I would pick E.
Actually I hesitated with D, but in fact I think that D actually support the conclusion.
With E we see that the soil texture and sunlight exposition were resposible for the higher yield.

My pick is E.

Argument says that Magnesium salt was the only thing that was different in both the plots.

E provides others reasons (soil texture and exposure to sunlight) were different in the two plots because which the tomato produce in plot would have been more than the produce in another plot.

A. Doesn't weaken the argument. It tries to confuse you making you think that if some salt leached then we would have similar results. But since a small amount leached it's not relevant enough.
B. Doesn't weaken the argument, just adds a different variable.
C. If they were grown in equal proportions then it strengthens the argument instead of weakening it.
D. It strengthens the argument: some weeds that compete with tomatoes died in the 1st plot while they may have grown in the second, affecting the yield of the second plot.
E. If true, it really weakens the argument, showing that we couldn't compare the two plots as equal, allowing other variables to play some effect on the yields.

E provides an alternate explanation for why we have different yields.

I go with E too
A: it kind of supports the argument...
B: out of Range
C: Out of Range
D: It kind of Supports the argument
E: This alone weakens as it talks about other parameters that might have affected the yields in both

+1 E

That option mentions other possible explanations.
Thats's the key in weaken questions which show causal relationships.

Its E all the way... Evrything else is irrelevant... E brings in the alternate cause for the increase in the tomato.. Thus casting doubt on the conclusion...

Conclusion: The higher yields in the first plot must have been due to the magnesium salts.

D) Some weeds that compete with tomatoes cannot tolerate high amounts of magnesium salts in the soil. strengthen the argument.

E)The two experimental plots differed from each other with respect to soil texture and exposure to sunlight. weakens the conclusion since it says that the quality of the soil of the second plot was not good and the second plot did no get sufficient sunlight.

The argument is that the higher 20lb yield in the first plot is due to the magnesium salts.

supported by the fact the same number of tomato plants were planted in each plot, Mg salts added to first and not second, and both plots received nothing but water.

Weaken

A - Incorrect - this wouldn't stand to weaken the argument. It doesn't weaken the position that magnesium salts were the only cause. If both plants received salts, but one received some more than the other then it would still stand that the salts were the cause.
B - incorrect- what happens to a third plot is not conducive to the deduction made regarding the first two plots.
C - Incorrect because another control factor - something applied to both plots - is discussed
D - Incorrect - some is fairly ambiguous. We don't know whether weeds were present in either plot. We would need to spin a bit of a story and assume a great deal to deduce that weeds were the cause of lower yields in plot 1. What if the only weeds that were presents in yield 2 were immune to magnesium? What if there were more weeds in plot 1 but these weeds were immune to magnesium?
E - Correct - points out a key difference that would could explain an alternate cause for the higher yields,

Two experimental plots A and B. Magnesium added to A, but not to B. Same number of tomatoes grown. Yield of A was better than B, in fact, double it was. Water was added to both the plots. On the basis of this yield and ignoring common factor like water, author concludes that magnesium might be the cause.

Well it logically seems right to conclude so, but there certainly might be many other factors about which we have no information. The idea should be to locate an option choice which could lower the weight of the assertion made by the author.

1) If small amount of Mg went into plot A from plot B, then the extra yield of A might not be completely attributed to Mg. But again, the amount is stated as "small". So , may be the its not 10 pounds extra because of Mg but only 7 or 8 pounds. Even then, one can conclude Mg is the cause, isn't it.... Not even a mild weakener.

2) If we see clearly, this statement adds 5 pounds to B by using fertilizer. But no fertilizer was added to plot A. Looks like even the fertilizer could not give as much yield as Mg could. This option only gives benefit of fertilizer but is unable to cast doubt on Mg being the underlying cause of the double yield.

3) In each plot, same proportion of 4 tomatoes types were grown . Does this statement change anything apart from ruling out a possibility of different tomatoes being grown in A and B, because if that would have been the case, it might have been possible that tomato type and not Mg was the cause of double yield. The option hence becomes a strengthener and not a weakener.

4) Okay, so some weeds which can reduce the growth level and hence yield of tomatoes, are harmed by Mg. If that is the case, it is possible that because Mg was introduced in plot A, that weed could not grow there and hence tomatoes grew better in A and not so much in B. But again ... do we actually know how much high was the Mg in plot A. Was it high enough to destroy the weed. Moreover, are we sure that the weed which we are talking about in this option was growing in those two plots. This option is, at best, a mild weakener only.

5) Now, here we are given two factors which could have influenced the yield of tomatoes because these factors were not kept the same for both plots. This option raises a concrete suspicion on the validity of the conclusion. A possible correct choice.

My answer, choice E

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