Vacuum cleaner salesperson: To prove that this Super XL vacuum cleaner

The Argument is about comparing 2 vacuum cleaners, Conclusion : Super XL is better than vacuum cleaner.

The vacuum cleaner salesperson's argument is most vulnerable to the criticism that it:

(A) Ignored the possibility that dirt remained in carpet even after the Super XL had been used in the test Not mentioned in the passage, In fact in passage it is stated that "All that that the Super XL picked up is dirt that your old vacuum left behind", Implying nothing is left

(B) Takes for granted that the Super XL will still perform better than the old vacuum cleaner when it is the same age as the old vacuum cleanerIrrelavent, We are not sure about Old once age as well.

(C) Takes for granted that because the Super XL outperforms one vacuum cleaner that it is the best vacuum cleaner available Conclusion never mentioned best, All it said was better VC.(Super XL > Old VC)

(D) Ignores the possibility that the amount of dirt removed in the test by the old vacuum cleaner is greater than the amount of dirt removed by the Super XL It seems like a promising choice, But we can't compare the amount of dirt picked as the initial conditions are different for both the VCs.

"Ignores the possibility that the amount of dirt removed in another test, where initial conditions were same, by the old vacuum cleaner is greater than the amount of dirt removed by the Super XL"
Had it been this way I would have picked this choice.

(E) Ignores the possibility that if the Super XL had been used first it would have left behind just as much dirt as did the old vacuum cleanerYeah If that is the case surely weaken the claim.

I agree this might not be a perfect choice as we are not sure the amount of dirt left behind if it goes first, I mean is the leftover dirt greater/less than the Old VC's leftover dirt


Feel free to correct my analysis. Thanks

Important to note that this is an LSAT flaw question - extremely common on the LSAT but relatively rare on the GMAT. For GMAT students, approaching these as weaken questions is perfectly acceptable.

That being said, the following represents what I teach LSAT students. Developed this independently, although others apply something similar (I think). My point: the only real evidence I have to support my approach is 90 official LSAT tests. Questions or criticisms are understandable and welcome because things are about to get weird.

NOTE 1: unlike the GMAT, the LSAT doesn’t test grammar. As most GMAT students know, the technical descriptions of grammar rules can be difficult to comprehend. The following includes a technically incorrect definition of the rule for the conjunction “that” in a sentence. However, the description is accurate, just designed for students not familiar with the strict rules of grammar.

NOTE 2: the following does NOT represent the entirety of my approach to weird Flaw answer choices. Not hiding anything, but this reply is long enough as it is. Any longer would be counterproductive

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Hypothesis: if an argument fails to consider THAT something weakens the argument, then that argument is flawed.

Similarly: if an argument ignores the possibility THAT something weakens the argument, then that argument is flawed.

BUT: if an argument takes for granted THAT something weakens the argument, then the argument isn’t flawed, just nonsensical (because an argument will never take for granted that something weakens it).

Note the emphasis on the word “that”, a part of speech with multiple functions. In the case of the Flaw answer choices discussed above, “that” functions as a conjunction introducing a complete sentence. That is, the phrase following “that” is a complete sentence on its own.

Specifically: “something weakens the argument” is a complete sentence.

NOTE: “fails to consider” and “ignores the possibility” will not always precede the conjunction “that” (extremely rare for the GMAT to do the same). In these cases, the following is not applicable.

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Implications

For answer choices that say “fails to consider THAT” or “ignores the possibility THAT”, ignore these phrases and focus on the complete sentence after the conjunction “that”. Reimagine the question as a weakener and determine whether that sentence weakens the argument.

This approach can be used with answer choices A, D, and E. Each of the following should be read as an answer choice to a weaken question.

(A) Dirt remained in the carpet even after the super XL had been used in the test.
This implies the super XL might not be a great vacuum cleaner, but based on the evidence/premises in the stimulus, it still appears to be better than the old vacuum.

(D) The amount of dirt removed in the test by the old vacuum cleaner is greater than the amount of dirt removed by the super XL.
This definitely looks to weaken the conclusion. Keep it (for now).

(E) If the super XL had been used first it would have left behind just as much dirt as did the old vacuum cleaner.
This also definitely looks to weaken the conclusion. Keep it (for now).

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Two ways to eliminate D and select E

(1) Ask yourself: WHY is the conclusion (the last sentence) is true? Your answer (the evidence/premises) should address the issue raised in E more than it does in D.

Put another way, E addresses the reasoning of the argument, but D doesn’t. GMAT CR and LSAT LR want an answer that addresses this reasoning. So regardless of whether D & E both appear to weaken the argument (even though D certainly does not), gotta select E.

(2) Everything in GMAT CR (and LSAT CR) should be taken literally, but no more and no less.

The conclusion doesn’t claim that the super XL picks up more dirt than the old vacuum cleaner. WTF?

The conclusion only claims that the super XL is better than the old vacuum cleaner. This immediately raises the question: what is meant by “better”? Picking up more dirt? Not according to the stimulus, which says nothing about how picking up more dirt “proves” (from the stimulus) a better vacuum cleaner.

According to the stimulus, “better” just means being able to pick up dirt not picked up by the old vacuum, as demonstrated in the example from the stimulus. But that’s just one example.

E flips the script on the example, indicating that the old vacuum performs the same way as does the super XL. That being the case, the super XL is certainly NOT proven to be the better vacuum.

Final NOTE: assuming that the above explanation for why E is correct is perfectly clear - students BEWARE! A major pitfall of studying for GMAT CR (and LSAT LR) is an over-reliance on understanding why all correct answers are correct and why all wrong answers are wrong.

Of course, once someone explains the logic behind right and wrong answers, everything makes perfect sense. Just like all those crazy-ass word problems in the Quant section. But the GMAT is not an “understanding” test it’s a “doing” test.

The point: the first way (described above) to eliminate D and select E is a better way to approach this stuff than the second way. Feel me?

Posted from my mobile device

Vacuum cleaner salesperson: To prove that this Super XL vacuum cleaner is better than your old vacuum cleaner, I ran your old vacuum once over this dirty carpet. Then I ran the Super XL over the same area. All that that the Super XL picked up is dirt that your old vacuum left behind, proving the Super XL is the better vacuum.

The vacuum cleaner salesperson's argument is most vulnerable to the criticism that it:

(A) Ignored the possibility that dirt remained in carpet even after the Super XL had been used in the test

(B) Takes for granted that the Super XL will still perform better than the old vacuum cleaner when it is the same age as the old vacuum cleaner

(C) Takes for granted that because the Super XL outperforms one vacuum cleaner that it is the best vacuum cleaner available

(D) Ignores the possibility that the amount of dirt removed in the test by the old vacuum cleaner is greater than the amount of dirt removed by the Super XL

(E) Ignores the possibility that if the Super XL had been used first it would have left behind just as much dirt as did the old vacuum cleaner - CORRECT. The sequence is questionable with context presented and conclusion made.

Only D stood some chance relatively but the amount part is an exertion of the context. What is left and sequence of usage is more important.

Answer E.
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