GMAT Tip: Navigating Negation on Assumption Questions

Photograph by Ingmar Wesemann

This tip on improving your GMAT score was provided by Brian Galvin at Veritas Prep.

Do you know that expression,”When you assume …?” Well, assumption questions on the GMAT have a way of making you (and me) look foolish, too—most would agree that assumption questions tend to be the most difficult among the critical reasoning varieties. Why?

It’s because in most questions, the correct answer takes the place of a “sword” attacking or advancing an argument. On a question that asks you to weaken a conclusion, the correct answer generally attacks that conclusion directly. On a question that asks you to strengthen a conclusion, the correct answer directly adds a new piece of information that makes the conclusion that much more likely to be true. But on assumption questions, almost by definition, the correct answer is something that doesn’t add a ton of new value; it’s something that many would have already expected, that they would have assumed.

Consider an example:

In the town of Hillsdale, the mayor reacted to the alarming rate of traffic accidents by lowering the speed limit by an average of 10 miles per hour from last year to this year. Traffic accidents this year are down by almost 20 percent, so clearly that plan has worked.

Which of the following is an assumption upon which the argument relies?

(A) Were it not for one particularly nasty ice storm, the accident rate would be down even more than 20 percent.

(B) The town’s police department has reported fewer traffic incidents this year than ever before.

(C) The number of drivers in Hillsdale was not significantly higher last year than it is this year.

Notice that both A and B could be considered “sword” answers. Either would help to advance the conclusion that this plan has worked. But neither is required by the argument. C is the correct response, but it’s not as “exciting” as the others. It takes the role of a “shield,” protecting the argument against attack. Here’s how:

The argument as it stands says that: (1) We passed a new law in the hopes of reducing accidents. (2) Since then, accidents are down. (3) The law worked.

Our only evidence that the law worked is the fact that the number of accidents is down. We need to protect that piece of evidence. Choice C does so by removing an alternate explanation for that statistic that would make it meaningless for the conclusion. If C were NOT true, and the number of drivers were significantly lower, then the conclusion would be in serious doubt. Was it the law, or just the fact that with fewer people on the road, the number of accidents would naturally have dropped anyway?

So recognize first that assumption questions are often much less obvious because they take the shield role, not the sword role. Second, that to succeed on difficult assumption questions, you will likely want to consider the opposite of the answer choices to see if the opposite is a direct threat to the argument. After all, the correct answer is a shield, so its opposite will be the sword. Here, a great “weaken” answer would have been “the number of drivers in Hillsdale significantly decreased from last year to this year,” providing an alternate theory for why the statistic was true but the law hadn’t had any bearing. That’s the direct opposite of choice C.

So in order to improve your accuracy on assumption questions, recognize that even though the correct answer will take the form of a shield, you can change the game by considering the argument that it’s defending.

Brian Galvin has studied the GMAT full time since 2006 as the director of academic programs for Veritas Prep. He received a Masters in Education from the University of Michigan and is the proud owner of a 99th percentile GMAT score.

For more GMAT advice from Veritas Prep, read “GMAT Tip: Strategy to Correctly Solve the Most Difficult Assumption Questions”

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