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GMAT Tip: Breaking Down a GMATPrep CR Evaluate A Conclusion Problem

Today’s GMAT tip comes from test prep firm ManhattanGMAT. In this article, they share helpful tips on how to solve critical reasoning problems that require you to evaluate a conclusion.  Read on to see what they have to say!

This week, we’re going to tackle a harder GMATPrep critical reasoning question from the Evaluate A Conclusion category.

Let’s start with the problem. Set your timer for 2 minutes!

* ”Capuchin monkeys in Venezuela often rub a certain type of millipede into their fur. Secretions of these millipedes have been shown to contain two chemicals that are potent mosquito repellents, and mosquitoes carry parasites that debilitate the capuchins. The rubbing behavior is rare except during the rainy season, when mosquito populations are at their peak. Therefore, the monkeys probably rub the millipedes into their fur because doing so helps protect them against mosquitoes.

“Which of the following would it be most useful to determine in order to evaluate the argument?

“(A) Whether the two chemicals provide any protection for the millipedes against their own predators

“(B) Whether the type of millipede used by the capuchin monkeys in Venezuela is found in other parts of the world

“(C) Whether animals other than capuchins rub insects of any kind into their fur

“(D) Whether the only time the millipedes are readily available to the capuchins is during the rainy season

“(E) Whether secretions of any other insects accessible to the capuchins contain chemicals that repel mosquitoes”

Okay, now that you’ve got an answer, we’re going to go back to the question stem and argument and forget about the answers for a moment. How do you identify the question type? What should you know about that question type before you even start to read the argument? What should you look for in the argument? What might your notes have looked like?

Reading the Question and Argument

First, if you haven’t already, you may want to take a look at this article: Strategies for Critical Reasoning.

As the article says, we read the question stem first. This is the question stem:

“Which of the following would it be most useful to determine in order to evaluate the argument?”

The key identifying language is pretty straightforward on this one: “evaluate the argument.” This language reflects an Evaluate a Conclusion problem type.

What kind of information is found in Evaluate A Conclusion questions and what are we supposed to do with that information?

Evaluate questions ask us to find the answer choice that can best help someone to determine whether a conclusion is more likely to be true or less likely to be true. It is not actually asking us to determine that the conclusion is more likely to be true or to find something that will help the conclusion to be true.

In this argument, the first sentence tells us a fact: certain monkeys rub a millipede into their fur. The second sentence tells us two more facts: the millipedes contain chemicals that repel mosquitoes, and mosquitoes are bad for the monkeys. The third sentence tells us yet another fact: the monkeys usually only do this during the rainy season when there are also lots of mosquitoes.

Finally, the last sentence presents the author’s claim: the monkeys undertake this action in order to protect themselves against mosquitoes.

Your notes might look something like this (though there are lots of ways to write notes!):

Mk rub mill when rainy —–>

Mill = anti-mosq —–>                    Mk rub mill to protect against mosq

Mosq bad for Mk + lots mosq rain —–>

What does this mean in normal, non-GMAT language? The monkeys are choosing to do something because it provides a certain benefit – that’s the author’s hypothesis (and this is often how these arguments are presented). The other information is evidence the author uses to try to support that claim.

Right now, let’s say I have the opinion that the author has made a decent case, but I can still think of some holes in his argument. What additional information could I be told that would make me think either that the hypothesis was less decent or that the hypothesis was more decent, depending upon the additional information given?

That’s really the question we’re trying to answer. Notice that the answer choices are all in the form of “whether <something is true>”. We can answer such a statement “yes” or “no.” Here’s a simpler example: I think you should take your umbrella. In order to evaluate my statement, you might ask whether it is raining outside. If the answer is yes, you’d be more likely to think I’m right, and if the answer is no, you’d be less likely to think I’m right. The correct answer should be the one for which, if the answer is “yes,” the conclusion gets a little better OR a little worse, and if the answer is “no,” the opposite thing happens to the conclusion (if it got a little better with a yes answer, it should get a little worse with a no answer and vice versa).

In particular, these types of arguments typically claim some kind of causal connection between one or more premises and the conclusion. Think of the conclusion as a hypothesis: the author is hypothesizing that the cause-effect relationship is true. The correct answer will let you further test that hypothesis – not to say that it is definitely true or false, but to say whether it is a little more or a little less likely to be true. Typically one of the premises will serve as the “final” piece of direct evidence to support the hypothesis – and we’re most interested in that premise.

Okay, now we know what we need to do. There’s just one more thing: the trap wrong answers for this question type.

On Evaluate questions, the most tempting traps typically address some part of the premises but don’t actually address the claimed causal connection between the premise and the conclusion. The answers look like they’re relevant (because they address something in the argument) – but they don’t actually address the right thing.

Answering the Question

To recap: we first want to find the causal connection between one or more of the premises and the claim / conclusion. Then, we want to find the answer choice that allows us to test that hypothesis – a “yes” or “true” answer should do one thing to the hypothesis, and a “no” or “false” answer should do the opposite.

In this problem, the claim (or hypothesis) is that the monkeys choose to rub millipedes into their fur on purpose in order to protect themselves against the mosquitoes. The direct evidence to support this is that the monkeys typically only take this action during the rainy season, when there are a lot of mosquitoes. That evidence is actually only a correlation – scientists notice these two things happening at the same time – but does not address possible causes or connections between the two.

Now, go through the answers and eliminate any that you think are definitely wrong. For any that might be right, don’t eliminate yet; save them for a later comparison.

Answer A talks about the millipedes protecting themselves against their own predators. Does that address the hypothesis? No. The hypothesis is specifically about the monkeys protecting themselves against the mosquitoes. This one is out of scope. Eliminate A.

Answer B talks about the location of the millipedes – whether they can be found in other places. Does that address the hypothesis? No. The hypothesis is specifically about certain monkeys located in Venezuela. This one is also out of scope. Eliminate B.

Answer C talks about whether other animals besides the capuchins exhibit the same type of behavior. Does that address the hypothesis? No. The hypothesis is specifically about certain capuchins exhibiting this behavior. This one is also out of scope. Eliminate C.

Answer D talks about the period of time when the millipedes are available for use by the capuchins. Does that address the hypothesis? Yes. The hypothesis does talk about when the capuchins use the millipedes. Leave this one in.

Answer E talks about what other insects the capuchins might use to protect themselves against the mosquitoes. Does that address the hypothesis? Yes. The hypothesis talks about why the capuchins take a certain action (to protect against mosquitoes) and how. Leave this one in.

A, B, and C are out. We need to examine D and E again. Often, at this stage, the distinction will hinge upon either (a) whether the answer addresses the specific leap between the main supporting premise and the conclusion / hypothesis, or (b) whether the two possible outcomes (yes or no) for the answer lead to opposite results when evaluating the hypothesis (a little more likely to be true versus a little less likely to be true).

The main supporting premise had to do with the fact that the monkeys only rub the millipedes on themselves during the rainy season, which is also when there are a lot of mosquitoes. Answer choice D appears to address that information; answer choice E does not talk about the timing of the monkeys’ actions. That’s a vote in D’s favor.

If we were actually able to know the information discussed in each answer, how would that information affect the hypothesis?

For D, if the millipedes are only available during the rainy season, then the monkeys can only engage in the behavior then. That is, the monkeys aren’t necessarily choosing to engage in the behavior specifically because they know mosquitoes are more prevalent during the rainy season. They don’t actually have a choice to do so at other times. That weakens the author’s hypothesis a little bit. If the millipedes are available at other times, but the monkeys only exhibit the behavior during the rainy season, then the monkeys are actually choosing to use the millipedes only at a certain time. That strengthens the author’s hypothesis a little bit. D passes our second test.

For E, if there are other available insects that can also help repel mosquitoes, then the monkeys could be using them, too – perhaps at different times than they use the millipedes. Does that make it more or less likely to be true that the monkeys are choosing to use the millipedes in order to protect against mosquitoes? Hmm. I’m not really sure. And if there aren’t other available insects? Still, I’m not sure how that affects the conclusion about the monkeys use of millipedes. So E fails this test as well.

The correct answer is D.

Key Takeaways for Solving Evaluate a Conclusion CR Problems:

(1) Know how to recognize this type. This is typically straightforward, as most of these will actually use the word “evaluate” in the question stem.

(2) Know what to do with Evaluate questions. Find the conclusion and identify the main supporting premise. If you can articulate any gaps between the main premise and the conclusion, do so. Think of the conclusion as the author’s hypothesis; your job is to find the answer choice that can test that hypothesis. The answers will provide a “whether or not” type of statement, indicating information that might or might not be so. The correct answer will be able to both slightly strengthen and slightly weaken the hypothesis, depending upon whether the information in that choice is true or is not true.

(3) Know what you’re not trying to do as well. We’re not trying to strengthen the conclusion or make it more likely that the author’s hypothesis is correct.

* GMATPrep questions courtesy of the Graduate Management Admissions Council. Usage of this question does not imply endorsement by GMAC.

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