Tackling a GMATPrep Critical Reasoning Weaken Problem


This week, we’re going to discuss one of the most common critical reasoning problem types: Weaken the Conclusion. If you haven’t yet, read this article before we try our GMATPrep problem. Then set your timer for 2 minutes and go!

* Tiger sharks are common in the waters surrounding Tenare Island. Usually tiger sharks feed on smaller sharks, but sometimes they have attacked tourists swimming and surfing at Tenare’s beaches. This has hurt Tenare’s tourism industry, which is second only to its fishing industry in annual revenues. In order to help the economy, therefore, the mayor of the island has proposed an ongoing program to kill any tiger sharks within a mile of the beaches.

Which of the following, if true, most strongly calls into question the likelihood that implementation of the mayor’s proposal will have the desired consequences?

(A) Even if not all the tiger sharks that come close to the beaches are killed, the existence of the program would reassure tourists.

(B) Business owners who depend on tourism are willing to pay most of the cost of implementing the program.

(C) Tourists come to Tenare Island for its beaches, even though the island features a number of other tourist attractions.

(D) The small sharks on which tiger sharks prey feed on fish that are commercially important to the island’s fisheries.

(E) Not all tourists who come to Tenare Island enjoy swimming or surfing.

Okay, now that you’ve got an answer, let’s use our 4-step CR process.

Step 1: Identify the Question

First, we read the question stem:

Which of the following, if true, most strongly calls into question the likelihood that implementation of the mayor’s proposal will have the desired consequences?

The key identifying language is not as straightforward as usual on this one. The language if true indicates that we probably have either a strengthen, weaken, or paradox question. (It’s possible to have a different question type, but if true language indicates one of these three types the vast majority of the time.)

The language indicates that the mayor has some kind of proposal with certain desired consequences “ basically, the mayor has a plan that is supposed to lead to some certain conclusion or outcome. The question asks us to call this into question “ in other words, we’re looking for something that’s going to weaken the conclusion.

Now we need to go read the argument and figure out what the mayor’s conclusion is!

Step 2: Deconstruct the Argument

In this argument, the first sentence is background information: a certain kind of shark lives in a certain region. The second sentence also contains facts. Now we know that tiger sharks normally eat other sharks, but they have been known to attack people. The third sentence contains more facts: the shark attacks have hurt tourism and tourism is important to the region (along with fishing).

Finally, we get to the conclusion in the final sentence. First, note the opening language: in order to help the economy. This is really important. Some plan is going to be proposed in order to help the economy. In other words, it’s pretty likely that helping the economy is the final conclusion. Read on. The mayor wants to kill the tiger sharks that are close to the beaches. Why? In order to help the economy.

Notice how they’re trying to trick us! The word therefore comes right before the plan to kill the sharks, not right before the in order to help the economy language, so it would be very easy to say that the plan itself is the conclusion. But why is the mayor implementing this plan? If the plan succeeds, then what will happen? The economy will get better in some way.

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

Usu: TS eat sm S
BUT st attk ppl → â†“ tour ind #2 (#1=fish)
© kill TS near bch → â†‘ econ

Note that I used abbreviations; you can use any you want as long as they make sense to you. My typical abbreviation for usually or normally is Usu: (with the colon after). It’s fairly common for an argument or RC passage to talk about how something is usually or typically done, so that’s why I have a standard abbreviation that I always use. (And I’m unlikely to confuse Usu: for some other word or meaning.) I use the abbreviation “st” to mean either sometimes or something (in this case, it means sometimes).I also used horizontal arrows to show when one thing led to another, and up and down arrows “ these can be used to show something that’s getting better or worse, or for quantities (more or less of something) and so on. Finally, I used a c with a circle around it to indicate the conclusion.

While I’ve been doing this, I’ve also been looking for assumptions. What are assumptions?

Assumptions are NOT stated in the argument, but they are things that the author (whoever’s drawing the conclusion) must believe to be true in order to draw that conclusion. In this case, the mayor is drawing the conclusion that killing the tiger sharks in the area will help the economy. What is the mayor assuming must be true?

The mayor is assuming that they can actually find and kill the tiger sharks. The mayor is assuming that there aren’t so many that they’ll just keep coming. The mayor is also assuming that killing the tiger sharks won’t have an unexpected consequence that could actually hurt the economy rather than help it. For example, what if tourists found out about the plan and decided not to vacation on the island in protest?

I don’t need to brainstorm all of the possible assumptions “ I don’t have time! “ but I do have some general ideas: the plan has to work in the way that the mayor is assuming it will, and the plan can’t have the unexpected consequence of hurting the economy in some way instead of helping it. These two generalities are often true on problems in which there is some kind of plan that is designed to lead to a specific goal.

Step 3: State the Goal

Our goal is to find an answer that makes the mayor’s plan a bit less likely to succeed. (On weaken questions, we do not have to find an answer the completely destroys the argument; it’s enough to make the conclusion less likely to be true or valid.)

Glance at the wording of the question again: it specifically asks us to find something that will hurt the ability to achieve the desired consequences. In other words: somehow, something will actually make it more likely that the plan would fail to help the economy. We need to find that thing.

Step 4: Work from Wrong to Right

(A) Even if not all the tiger sharks that come close to the beaches are killed, the existence of the program would reassure tourists.

Let’s see. We put the plan into place. We kill some sharks. We can’t kill all of them, but the tourists are reassured. This would be likely to help tourism, which would help the economy. That doesn’t weaken the conclusion. Eliminate A. (This is a Reverse Logic trap: we want to weaken the conclusion; this answer strengthens the conclusion.)

(B) Business owners who depend on tourism are willing to pay most of the cost of implementing the program.

Oh, that’s interesting: maybe the flaw in the plan is that it will cost money and so that will hurt the economy somehow! Hmm. Wait, but this says that the business owners are willing to pay the costs, not that they’re protesting the costs. That doesn’t hurt the mayor’s plan; in fact, it sounds like the business owners approve of the plan! Eliminate B.

(C) Tourists come to Tenare Island for its beaches, even though the island features a number of other tourist attractions.

If the tourists do vacation here primarily in order to go to the beach, then the tiger shark problem is definitely a big problem “ they’d better solve it! But they already know that; that’s why the mayor is proposing this plan. If nobody cared about the beaches or the tiger shark problem, then they wouldn’t have to bother implementing this plan. This doesn’t weaken the idea that the plan will succeed. Nor does it strengthen the idea. This choice just does nothing at all to the conclusion. Eliminate C.

(D) The small sharks on which tiger sharks prey feed on fish that are commercially important to the island’s fisheries.

This one kind of seems like it’s out of left field. Who cares about the small sharks that the tiger sharks eat? Let’s see. The tiger sharks normally eat these small sharks, and the small sharks normally eat fish that the fisheries are using or catching. So the small sharks are actually bad for the fishing industry because they eat up the fish. So what?

Oh, I think I see. Right now, the tiger sharks may be keeping the population of the smaller sharks under control “ there aren’t too many because the tiger sharks are eating them. If we get rid of all of the tiger sharks, then the smaller sharks will likely start increasing in number, which means they’ll be eating more fish, which means bad for the fishing industry. And the fishing industry is a major part of the economy; in fact, according to the argument, the fishing industry is even more important than the tourist industry. (Notice that the conclusion only says we’re trying to help the economy “ overall. It doesn’t say that we’re only trying to help the tourist economy!)

Wow, really? I’m a bit unsure whether I can really take that many steps. But the first three were definitely wrong. Well, I’ll leave this one in for now and check answer E.

(E) Not all tourists who come to Tenare Island enjoy swimming or surfing.

Okay, maybe some people don’t really care about the tiger sharks because they’re not there to use the beach. How does that affect whether the mayor’s plan will work?

It doesn’t. It doesn’t address the plan at all “ this answer is out of scope. They’re trying to get us to think Oh, maybe the shark thing isn’t such a big problem after all, because some people don’t care about the beach. But the argument flat-out told us that the tourism industry is already being hurt, and the question asked us to find something that weakens the mayor’s specific plan. This answer doesn’t address any of that. Eliminate E.

The correct answer is D.

Okay, raise your hands: how many of you eliminated D because it seemed like it was going way too far “ totally out of the scope of the argument? This is a tough question; I’m sure a lot of people eliminated D for this or other reasons. How do we make sure that we’re not eliminating too quickly?

First, when you have a strengthen, weaken, or paradox question, be aware that the correct answer will be more out of scope than we’re allowed to be for other question types. Answers to inference and find an assumption questions have to be very tightly tied to the original information, but strengthen, weaken, and paradox questions are actually asking us to find a new piece of information to insert into the argument. So resist the urge to eliminate something immediately because you think it’s out of scope “ check to make sure.

How do we check? Glad you asked. = ) On strengthen and weaken questions, we’re specifically asked to strengthen or weaken the conclusion. First, then, we have to make sure we find the conclusion. Second, we have to examine the answers from the point of view of how they affect the conclusion.

Answer E was truly out of scope because it did not affect the conclusion (whether the plan would or would not help the economy). Answer D, on the other hand, was very much in scope, because it did affect the conclusion: if answer D is true, then it’s somewhat less likely that the plan will actually succeed in its goal to help the economy. It might help the tourist economy, but at the expense of the fishing economy “ which is the #1 source of annual revenues.

Key Takeaways for Solving Weaken CR Problems:

(1) Know how to recognize this type. The question stem will contain if true or equivalent language, as well as language such as most weakens, most seriously undermines, casts the most doubt, calls into question, or something similar.

(2) Know what to do with Weaken questions. Find the conclusion and identify the main supporting premise(s), then brainstorm assumptions. Our goal is to find an answer that makes the conclusion at least a little less likely to be true. We don’t need to find an answer that completely destroys the conclusion.

(3) Watch out for traps! These questions usually contain a Reverse Logic trap (they ask us to weaken, and the answer strengthens instead, or vice versa). In addition, be careful not to eliminate too quickly because you think something is out of scope. Check to see whether it affects the conclusion in any way. It’s only out of scope if it does not affect the conclusion. (If it does affect the conclusion, then that answer either weakens or strengthens the conclusion.)

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

  1. Manhattan Prep May 3, 2016 at 6:31 pm

    Hi, Manjunath.

    You might be mixing up question types. This is a Weaken question type – which means that the correct answer is supposed to contain new information. We are supposed to accept the information in the answers as true (note the words “if true” in the question stem) and then use that new information to evaluate the argument. The correct answer will, if added to the argument, serve to weaken that argument.

    In other words, IF it is true that (D) the small sharks feed on even smaller fish that are important to the fisheries, THEN it is less likely that the mayor’s proposal will achieve its stated goal to help the economy – because then the fisheries industry will be hurt and the fisheries industry is even larger than the tourism industry. Therefore, yes, the mayor’s argument is weakened and (D) is the correct answer.

    Are you thinking about a Find the Assumption question? That type of question would place assumptions in the answer choices and ask you to find the one that the argument already assumes to be true. That’s a different question type – it does not ask you to introduce new information into the argument in order to evaluate that argument.

    I would recommend learning what each CR question type is asking you to do and what rules you are expected to follow for that specific type of question. That’s half the battle on CR!

    Manhattan Prep

  2. Manjunath May 1, 2016 at 7:24 pm

    Why do you assume that the smaller sharks feed on the fish which would eventually affect the fishing industry? There is no mention whatsoever in the passage that the smaller sharks are a threat to the fishing industry. It could be possible that the tiger shark eats smaller sharks and ten times of the tiny fish too(assumption). I didn’t find D conclusively correct either.

  3. Business School Admissions Blog | MBA Admission Blog | Blog Archive » GMAT Impact: All About Critical Reasoning, Part 1 June 28, 2013 at 11:54 am

    […] […]

  4. google December 28, 2012 at 10:42 am

    wow, Im viewing your blog and my brother is reading the same post on the iphonei guess youre a pretty good blogger lol

  5. brand December 23, 2012 at 1:17 pm

    You make some good points. I guess it depends on your standpoint. In two words, im possible. Samuel Goldwyn 1882 1974

  6. brand December 23, 2012 at 1:17 pm

    Thanks for taking the time to write about this issue. I really appreciate it. I’ll post a link of this post in my blog.

  7. brand December 22, 2012 at 8:07 am

    Great websiteand cool article manthanx for the great postkeep on posting such article

  8. GMATcheetah April 29, 2012 at 11:05 pm

    Thanks Stacey!

  9. anu April 10, 2012 at 8:10 am

    Amazing article..clearly understood the concept.
    Thanks a ton 🙂

  10. Shashank April 3, 2012 at 11:11 pm

    good explanation !!!

  11. vj February 16, 2012 at 10:58 am


  12. Rajesh Hariharan February 16, 2012 at 7:35 am

    Lovely !!! I liked the Q but did not eliminate D …

  13. Rajesh Hariahran February 16, 2012 at 7:34 am

    Lovely !!! I liked the Q 😀 but did not eliminate D 🙂 …