#5 - Motor oil serves to lubricate engines and thus retard

[Administrator]

Complete Question Explanation

Weaken. The correct answer choice is (E)

Since all brands of motor oil did equally well in retarding wear on pistons and cylinders, the author concludes that cheaper brands of oil are the best buys. This may be so, as long as the oil's ability to retard wear on the engine is the only factor relevant to consumers. What if motor oil has other important functions, such as inhibiting corrosion or cooling the engine, that should be taken into account when determining its effectiveness? If the cheaper oils score a lot lower in inhibiting corrosion, for instance, they might not ultimately be the best buys.

Answer choice (A): This answer choice does the exact opposite of what is needed — it strengthens the proposition that cheaper brands of motor oil are the best buys. This answer choice is incorrect.

Answer choice (B): Since we don't have the results of any other tests that can be used to gauge the quality of motor oil, this answer choice has no effect on the author's conclusion and is incorrect.

Answer choice (C): The fact that all motor oils suffer from deterioration over time strengthens the idea that buyers may be better off buying cheaper brands. This answer choice is incorrect.

Answer choice (D): This seems to be an attractive answer choice at first, as it implies that a certain brand of motor oil is particularly effective in ensuring that engines last a very long time. There are three problems with this line of reasoning: first, we have no idea how expensive this brand of oil was: if it was cheaper than the rest, this result would strengthen the author's logic, not weaken it. Second, it is entirely possible that the beneficial effects observed stemmed not from the high quality of oil used but merely from the increased frequency with which it was changed. Third, we have no way to compare how the different brands of oil would have fared had they been changed every 3,000 miles, instead of every 6,000. This answer choice is incorrect.

Answer choice (E): This is the correct answer choice. If the ability to retard engine wear is not the only factor owners should take into account when purchasing a brand of oil, then more expensive brands may prove to have superior properties that are just as important to the running of an engine as the ability to retard wear.

[Blueballoon5%]

33. Motor oil serves to lubricate engines...

Which one of the following most weakens the argument

B) Tests other than the ability..
E) Ability to retard engine wear...


My question: I really can't see the difference between the answer choice B and E. The answer in the student online center explained that answer B is wrong because "Since we don't have the results of any other tests that can be used to gauge the quality of motor oil, this answer choice has no effect on the author's conclusion and is incorrect." I don't understand how this would disqualify B -- couldn't there still be a possibility that the tests results would weaken the argument?

For answer choice E, I also don't understand how this could be the right answer. Although the ability to retard engine wear is not the only important property, doesn't this leave the possibility that the cheaper choices also have the best of other properties. Or that all choices have the same qualities?

[BethRibet]

Hi Blueballoon,

Thanks for writing.

Answer choice B could be true, and still not really weaken the argument, because even if true, answer choice B doesn't indicate that there's anything wrong or unreliable about the original test in question. B would be stronger if it at least indicated that these other tests are much better, or that the test used was not always accurate, for instance. For instance, if someone concluded, "The LSAT best measure of whether a person should go to law school", and you then added an answer choice that says "The are other ways to test preparedness for law school", this doesn't weaken the conclusion -- but because it doesn't attack the idea that the LSAT is still the best option. The fact that it might possibly be true that these other tests could be better isn't enough, the answer choice would need to actually say that, or at least clearly imply it.

Answer choice E does weaken the conclusion because it points out a flaw in relying on this test to draw a conclusion about the best motor oil -- namely that the test only tested for one property that the motor oil needs to have. While it might give helpful information, if it doesn't test for other properties the oil needs to have, then we don't have enough evidence to draw conclusions about which oil is ultimately best.

I hope that helps!
Beth

[Blueballoon5%]

Thanks so much! It does help a lot

[Dianapoo]

Complete Question Explanation

Answer choice (D): This seems to be an attractive answer choice at first, as it implies that a certain brand of motor oil is particularly effective in ensuring that engines last a very long time. There are three problems with this line of reasoning: first, we have no idea how expensive this brand of oil was: if it was cheaper than the rest, this result would strengthen the author's logic, not weaken it. Second, it is entirely possible that the beneficial effects observed stemmed not from the high quality of oil used but merely from the increased frequency with which it was changed. Third, we have no way to compare how the different brands of oil would have fared had they been changed every 3,000 miles, instead of every 6,000. This answer choice is incorrect.

Hi there!

The key to (D) actually being a good weakener is being sensitive to the use of the word "only" (I'm kinda going against the grain here).

Thus I'm not in total agreement here with Administrator's explanation! it says that using ONLY a certain brand helped the car so much at 3000km. So even if the other oils were applied under the 3000km conditions, this one would still do the best since "ONLY a certain brand helped the car so much". Also, your explanation seems to fall short in that the price of the wonder brand in (D) is irrelevant. It weakens the conclusion because it demonstrates that there is a difference between the effectiveness of various oils used. And the mere fact that there is a difference in effectiveness between various oils weakens the conclusion drawn since it is not necessarily true any more that cheaper brands are the best buys. This is actually quite similar to E, where it becomes not necessarily true any more that cheaper brands of oil are the best buys.

With all that said, I think that a lot of forums miss a big point about these kinds of questions. There can be multiple weaken answers, but one would MOST weaken. I'm always seeing everyone trying to explain why all the other answers don't weaken, and this is a flawed approach.

E is a more clear cut answer, but D is absolutely a weakener. So for anyone who chose D, well done but read E as well to see how it's a bigger weakener than D.

[James Finch]

Hi Diana,

I just want to quickly clear up a misconception: Weaken questions, just like Strengthen questions, are written to have only one correct answer. While the way the question stem is written does allow for some wiggle room, the incorrect answer choices should never weaken or strengthen the conclusion by themselves (that is, without bringing in outside assumptions).
And while the correct answer may do very little to actually weaken/strengthen the argument, the other answer choices will all either be irrelevant, or do the opposite of what is needed (ie weaken Strengthen questions or vice versa)

Here, we have a Weaken question, meaning we will have 4 answer choices that strengthen or are irrelevant to the conclusion. (A) would strengthen the conclusion, while (B), (C) and (D) are all irrelevant to the conclusion, leaving only (E) as the correct choice. The reason (D) is irrelevant is that it brings in a different test (having oil changed at 3K miles) and doesn't tell us what happens with other brands of oils under the same testing conditions. Moreover, it doesn't even tell us whether the brand of oil is cheap or not, nor give us very precise results ("some engines"). So it isn't helpful in attacking the stimulus, while (E) helps by establishing other factors that would cast doubt on using only the 6k mileage test to determine whether certain motor oils are good buys or not.

Hope this clears things up!

[catherineshi99]

Hi,

I still don't understand how B) and E) are different. Couldn't the same logic that "we don't have the results of any other tests" also apply to E)? Like even if E is true, it could be that the cheap oil has the same or better results in the other properties too.

If someone could help me understand this that would be great.

Thanks

[Beatrice Brown]

Hi Catherine! Happy to help you out with this

To best understand why answer choice (E) is correct, let's break down the stimulus to figure out any potential issues with the argument so that we can prephrase the correct answer choice:
Premise 1: Motor oil helps slow engine wear since it acts as a lubricant.
Premise 2: A study assessed how effective various brands of motor oil were and found that all of them did equally well in slowing wear on relevant parts of the engine.
Conclusion: Since all of them were equally effective, cheaper brands of oil are the best buys.

The issue with this argument is that the author draws a conclusion about which oils are the best buy based on one factor: the ability of the oil to slow engine wear. However, what if other factors were also relevant to which oil is the best buy? Maybe cheaper oils have a major drawback aside from their ability to slow engine wear, so they wouldn't be the best buy.

To weaken the conclusion, we want to find an answer choice that exploits this flaw. Answer choice (E) does so and matches our prephrase: there are other properties of motor oils that are important. If other properties are also important, then maybe cheaper oils aren't the best buy. Although you're right that cheap oil may have the same or better results for these other properties, we don't know this from the evidence given in the stimulus. In fact, this is exactly the issue: cheap oils may be better for these other properties, but they may also be worse, and if they're worse, then they're not the best buy and the conclusion is incorrect.

Answer choice (B), on the other hand, tells us that there are also other tests that can reliably gauge the quality of motor oil. However, just because there are other reliable tests doesn't mean that the test referred to in the stimulus is a poor way to gauge quality. Furthermore, this doesn't get at the core issue in the stimulus, which is the gap between the premises and the conclusion. We want to find an answer choice that exploits the gap between all oils doing an equally good job at slowing engine wear and cheaper oils therefore being the "best buy," and this answer choice does not do that.

To sum up, prephrasing is an extremely valuable tool for Weaken questions, because it helps us look for the gap between the premises and conclusion that we want to exploit when looking for the correct answer choice. Here, our prephrase matched answer choice (E), the correct answer choice.

I hope this helps, and please let me know if you have any other questions!

[ashpine17]

so is argument assuming retarding engine wear most important function of motor oil?

[Robert Carroll]

ashpine17,

As the explanation up top says, the argument is certainly assuming that ability is the only factor relevant to consumers.

Robert Carroll