Comprehension Flashcards
Manufacturers of motor oil for car engines have found through research that motor oil slowly loses lubrication effectiveness after the car is driven for certain distances. On average, the motor oil is only 50 percent as effective after 3,000 miles of driving as it is the first day it is put into the car. For that reason, people should replace their motor oil every 3,000 miles.
Which of the following, if true, would most weaken the conclusion above?
The research indicates that the oil loses effectiveness because it becomes dirty.
The researchers found that there was not a significant difference in the effectiveness of motor oil in cars that reached 3,000 miles quickly versus those that took a long time to reach 3,000 miles.
The researchers found that cars with motor oil at 50 percent effectiveness showed no more signs of damage or wear than those with fresh motor oil.
The researchers were paid by the manufacturers of motor oil, who have a vested interest in selling more motor oil.
Both synthetic and non-synthetic motor oils experience similar losses in lubrication effectiveness after 3,000 miles of driving.
(C) matches the prediction and is correct. If 50% effectiveness is enough to match the performance of fresh oil in preventing engine wear, this makes it less likely oil would have to be replaced at 3,000 miles.
The question directly asks for something that weakens the argument, making this a Weaken question.
The author concludes that motor oil should be changed every 3,000 miles, because after 3,000 miles it is only 50% effective.
The author is assuming that, once oil becomes only 50% effective, it needs to be changed. The correct choice will counter that assumption, showing that there it may not be necessary to replace motor oil when it becomes only 50% effective.
(A) is irrelevant. The author is not concerned with why the oil loses its effectiveness but whether that loss warrants changing the oil.
(B) is irrelevant. It does not matter how long it takes to reach the 3,000-mile threshold. The only question is whether or not the oil needs to be changed at that point.
(D) may be tempting, but it is irrelevant. A choice like (D) that questions the motives for the research may seem to weaken the argument. However, the evidence in a Weaken question can never be challenged - only the central assumption. Who supervised the research is not an issue. The argument is only concerned with the reduction in effectiveness and the recommendation to replace motor oil after 3,000 miles.
(E) is an irrelevant comparison between two types of oil and has no effect on the argument.
