Motor oil serves to lubricate engines and thus retard engine

Question

Motor oil serves to lubricate engines and thus retard engine wear. A study was conducted to assess the effectiveness of various brands of motor oil by using them in taxicabs over a 6,000-mile test period. All the oils did equally well in retarding wear on pistons and cylinders, the relevant parts of the engine. Hence, cheaper brands of oil are the best buys.

Which one of the following, if true, most weakens the argument?

Which one of the following, if true, most weakens the argument?

(A) Cheaper brands of motor oil are often used by knowledgeable automobile mechanics for their own cars.
(B) Tests other than of the ability to reduce engine wear also can reliably gauge the quality of motor oil.
(C) The lubricating properties of all motor oils deteriorate over time, and the rate of deterioration is accelerated by heat.
(D) The engines of some individual cars that have had their oil changed every 3,000 miles, using only a certain brand of oil, have lasted an extraordinarily long time.
(E) Ability to retard engine wear is not the only property of motor oil important to the running of an engine.

KarishmaB · Accepted Answer

The fact that there are some other tests also that could have been used to gauge the quality does not weaken the result obtained from this test. 
All we are given in the argument is that test A was conducted to find how well different brand oils retard wear in engines. It was found that all do a similar job. 
So the author concluded that buy the cheapest oil.

(C) Say tests B, C and D can also be used to gauge the quality of oil.

Doesn't mean that test A was not accurate. Hence this option does not weaken the conclusion.

(E) Ability to retard engine wear is not the only property of motor oil important to the running of an engine.

This option tells us that though under test A (used to gauge the oil's effectiveness in retarding engine wear) all oils seem to perform the same, there are other parameters on which they need to be judged too. So the author cannot arrive at the blanket conclusion 'just buy the cheapest oil'. That is why it weakens the conclusion.

shivimonji · Answer

Conclusion :- Since oil brands effect the engine in same way therefore cheaper brands are best buys.

Type:- Weaken We have to find an option that will tell that cheaper brands are not the best buy..

Link- What if wear and tera of engine is not the only way to gauge whether the oil is best buy

Thiis is what option E does.

Shubham2599jain · Answer

Can someone please explain why not B?  KarishmaB

miag · Answer

Hi,

The underlying hidden assumption is:  Retarding engine wear is the only property that matters when deciding which oil is the best buy.

(B) says:
 
 Other tests  exist  
 They  can  measure quality  
But it does not say:
 
 Those qualities matter to engine performance 
 Those qualities differ between oils 
 Those qualities would overturn the conclusion  
So even if B is true:
 
 The study could still be sufficient 
 Wear could still be the only thing that matters for  best buy.

>> While B) introduces additional information, it doesn't weaken

Hope this helps!

guddo · Answer

Motor oil serves to lubricate engines and thus retard engine wear. A study was conducted to assess the effectiveness of various brands of motor oil by using them in taxicabs over a 6,000-mile test period. All the oils did equally well in retarding wear on pistons and cylinders, the relevant parts of the engine. Hence, cheaper brands of oil are the best buys.

Which one of the following, if true, most weakens the argument?

Which one of the following, if true, most weakens the argument?

The argument concludes that cheaper motor oils are the best buys because, in a short test, all oils performed equally well in reducing engine wear on key parts.

(A) Cheaper brands of motor oil are often used by knowledgeable automobile mechanics for their own cars.

This actually supports the conclusion. If knowledgeable mechanics use cheaper oils, that makes cheaper oils look more attractive, not weaker.

(B) Tests other than of the ability to reduce engine wear also can reliably gauge the quality of motor oil.

This points out that there are other tests, but it does not say those tests matter for deciding what the best buy is. By itself, it does not weaken the conclusion.

(C) The lubricating properties of all motor oils deteriorate over time, and the rate of deterioration is accelerated by heat.

This talks about deterioration over time, but the argument is not comparing long-term performance differences across brands. It does not directly challenge the inference made.

(D) The engines of some individual cars that have had their oil changed every 3,000 miles, using only a certain brand of oil, have lasted an extraordinarily long time.

This is anecdotal and brand-specific. It does not show that the test used in the argument was inadequate or misleading.

(E) Ability to retard engine wear is not the only property of motor oil important to the running of an engine.

This directly weakens the argument. The conclusion assumes that retarding engine wear is the only relevant criterion for deciding the best buy. If other properties of motor oil also matter, then equal performance on wear alone is not enough to justify choosing cheaper brands.

Answer: (E)

guddo · Answer

B only says that other tests exist. It does not say those tests matter or that cheaper oils would perform worse on them, so the conclusion still holds.

E works because it says engine wear is not the only important factor, which directly undercuts the reason for calling cheaper oils the best buys.

agrasan · Answer

Hi  KarishmaB   MartyMurray

(D) The engines of some individual cars that have had their oil changed every 3,000 miles, using only a certain brand of oil, have lasted an extraordinarily long time.

How can we eliminate (D)? My reasoning was that it weakens the argument because if some engines were given oil every 3k miles then it casts a doubt that cheaper brands were somehow responsible to improve the retardation.

Please help me with the correct reasoning to eliminate (D).

miag · Answer

Hi, Let me try to help out with this one: (D) does not challenge the argument’s logic. Showing that one brand worked well in a few cases does not show that cheaper brands are worse or that wear reduction is an insufficient basis for comparison. (D) never links engine longevity to oil quality alone, nor does it compare that brand with cheaper oils. Further, the long engine life could be due to frequent oil changes (every 3,000 miles), good maintenance, or other factors unrelated to oil quality. Hope this helps!

guddo · Answer

D does not weaken because it does not connect “extraordinarily long life” to the oil being better.

It is just an anecdote about some cars, and it mixes in a big confounder: those cars had very frequent oil changes (every 3,000 miles). Their long life could be due to maintenance schedule, driving conditions, engine model, etc. So it does not show that the taxi test was misleading, and it does not show that cheaper oils are not the best buy.

To weaken the argument you need something that says: equal wear performance in that test is not enough to judge “best buy.” That is what E does.

KarishmaB · Answer

(D) adds a new parameter - how frequently the oil was changed. With a certain brand, changing oil every 3k miles led to engines lasting an extraordinarily long time. Was this because of the brand of oil or because it was changed every 3k miles? Perhaps the same thing will happen with any other oil brand that is also changed every 3k miles - we don't know. Hence this option doesn't impact the conclusion. 
Also it uses ' some individual cars.' A few exceptions do not weaken a general statement that holds on average.

MartyMurray · Answer

Motor oil serves to lubricate engines and thus retard engine wear. A study was conducted to assess the effectiveness of various brands of motor oil by using them in taxicabs over a 6,000-mile test period. All the oils did equally well in retarding wear on pistons and cylinders, the relevant parts of the engine. Hence, cheaper brands of oil are the best buys.

Which one of the following, if true, most weakens the argument?

Conclusion of the argument:

cheaper brands of oil are the best buys

Support for the conclusion:

Motor oil serves to lubricate engines and thus retard engine wear. A study was conducted to assess the effectiveness of various brands of motor oil by using them in taxicabs over a 6,000-mile test period. All the oils did equally well in retarding wear on pistons and cylinders, the relevant parts of the engine. Hence, cheaper brands of oil are the best buys.

Which one of the following, if true, most weakens the argument?

We see that the reasoning of the argument is the following. Various brands of oil, some of them presumably cheaper than others, did equally well in retarding wear on pistons and cylinders. So, since the cheaper brands cost less while producing the same results, they are the best buys.

Which one of the following, if true, most weakens the argument?

This is a Weaken question. So, the correct answer will indicate that, even though the evidence is true, the conclusion may not be.

(A) Cheaper brands of motor oil are often used by knowledgeable automobile mechanics for their own cars.

The fact that "knowledgeable automobile mechanics" often use cheaper brands tends to indicate that cheaper brands work well and thus are the best buys.

So, this choice is in line with the conclusion of the argument.

Eliminate.

(B) Tests other than of the ability to reduce engine wear also can reliably gauge the quality of motor oil.

The wording of this choice, " also can  reliably gauge the quality of motor oil," suggests that the test mentioned in the argument can reliably gauge the quality.

So, if anything, this choice bolsters the support for conclusion.

Eliminate.

(C) The lubricating properties of all motor oils deteriorate over time, and the rate of deterioration is accelerated by heat.

This information is about "all motor oils," including cheaper ones and more expensive ones.

So, it is not a reason to believe that cheaper ones are not as good as more expensive ones, and thus it has no effect on the case for the conclusion.

Eliminate.

(D) The engines of some individual cars that have had their oil changed every 3,000 miles, using only a certain brand of oil, have lasted an extraordinarily long time.

This information indicates that changing oil frequently, every 3000 miles, and using "a certain brand" may help engines last for a long time

OK, great, but this choice doesn't indicate anything about whether cheaper oils are as good as more expensive ones.

After all, it doesn't say whether the "certain brand" mentioned was cheaper or more expensive.

Also, even if it did, the "extraordinary" results mentioned could have be due to the high frequency of the oil changes.

So, this choice does not add any information that could be used for comparing cheaper and more expensive oils and thus has no effect on the case for the conclusion.

Eliminate.

(E) Ability to retard engine wear is not the only property of motor oil important to the running of an engine.

This choice is interesting.

After all, if "Ability to retard engine wear is not the only property of motor oil important to the running of an engine," then the fact presented by the passage, that "All the oils did equally well in retarding wear on pistons and cylinders," isn't complete information.

In other words, it could be that, even though cheaper oils did just as well as more expensive ones in retarding wear on pistons and cylinders, cheaper oils are not better buys than more expensive ones because cheaper oils are not as good as more expensive ones in terms of the other properties "of motor oil important to the running of an engine."

So, this choice serves to cast doubt on the conclusion by indicating that it may not be true because the supporting information does not cover all the important properties of motor oils.

Keep.

Correct answer:   E

Motor oil serves to lubricate engines and thus retard engine

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Motor oil serves to lubricate engines and thus retard engine

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