GMAT: Traps for Weaken Questions in Critical Reasoning:

by on March 23rd, 2018

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This is a really interesting question. I’m not going to tell you why yet, though.

Try this problem from the free GMATPrep© exams and then we’ll talk about what’s going on!

“Insect infestations in certain cotton-growing regions of the world have caused dramatic increases in the price of cotton on the world market. Knowing that cotton plants mature quickly, many soybean growers in Ortovia plan to cease growing soybeans, the price of which has long been stable, and to begin raising cotton instead, thereby taking advantage of the high price of cotton to increase their income significantly at least over the next several years.

“Which of the following, if true, most calls into question the reasoning on which the plan is based?

“(A) The cost of raising soybeans has increased significantly over the past several years and is expected to continue to climb.

“(B) Tests of a newly developed, inexpensive pesticide have shown it to be both environmentally safe and effective against the insects that have infected cotton crops.

“(C) In the past several years there has been no sharp increase in the demand for cotton and for goods made out of cotton.

“(D) Many consumers consider cotton cloth a necessity rather than a luxury and would be willing to pay significantly higher prices for cotton goods than they currently pay.

“(E) The species of insect that has infested cotton plants has never been known to attack soybean plants.”

Let’s start by talking about what you need to do for Weaken questions in general. Then we’ll tackle the problem.

Weaken questions are part of the Assumption Family (Assumption, Strengthen, Weaken, Evaluate, or Flaw). Any arguments in this family will provide you with some kind of premise(s) and conclusion. The argument will be making at least one assumption—something the author assumes to be true in drawing her conclusion even though she doesn’t explicitly state this assumption in the argument. Usually, there’s more than one assumption, and one of the unstated assumptions is going to be the key in solving the problem.

Let’s see how this plays out in the above problem.

 Step 1: Identify the Question

How do you know that this is a Weaken question in the first place?

Read the question stem. The wording calls into question indicates that this is a Weaken question. The question stem tells you something else, too: this argument contains some kind of plan. So your job is to find something that weakens the plan, whatever that is.

The question stem also includes the words if true—which you’ll find in the vast majority of strengthen, weaken, and discrepancy questions. This is signaling that the answers are going to contain new information and that this is okay. You are, in fact, looking for a new piece of information that will serve to weaken the plan.

Step 2: Deconstruct the Argument

What’s the basic story? Insects have caused dramatic increases in the price of cotton.

(Why might this happen? The insects are presumably eating or damaging the cotton in some way and, as a result, the farmers aren’t able to produce as much cotton. If the demand stays the same, then the prices are going to go up. Classic scarce-supply to increased-demand. You don’t need to think all of this—but it can help to understand how the argument works.)

So some soybean growers have decided to jump on the bandwagon! They’ll switch to raising cotton, which matures quickly, and gain some of those higher revenues for at least a few years.

Insect → ↑↑ price C

Soy: switch to C (fast grow)

 © Sig incr rev for few years

Here’s what’s so interesting about this problem. The argument didn’t explicitly say that the farmers would increase their profits. It simply says: Cotton prices have gone up a lot, so they’re going to switch in order to increase their income (revenue). If you (naturally) think profits, then you risk falling into a trap on this one.

Finally, what does this argument assume to be true?

At the very least, the price of cotton has to remain high for at least a few more years.

Step 3: State the Goal

On Weaken questions, the goal is to find the answer that, if true, makes the argument at least a little less likely to be valid. In this case, we’re looking for something that will weaken the soybean growers’ plan. What would make it less likely that they’ll be able to capitalize on the high price for cotton?

Hmm…will that price stay high? Either the situation has to stay the same (insects causing the cotton yield to go down, high demand for cotton) or something else has to cause a high demand for cotton. Otherwise, the soybean farmers’ plan isn’t looking too good.

Step 4: Work from Wrong to Right

All right, let’s dive in.

“(A) The cost of raising soybeans has increased significantly over the past several years and is expected to continue to climb.”

The first time I read this, I almost went too fast. It’s talking about the cost of raising soybeans, not the cost of soybeans themselves (which would translate to revenue for the farmers). If soybeans keep costing more and more to raise, then the farmers are probably smart to switch to cotton. If anything, this strengthens the argument, so it’s not the correct answer.

(Note: Even if this choice had said the cost of soybeans, the question asks you to weaken the plan to switch to cotton. This choice doesn’t help you to address that specific plan.)

“(B) Tests of a newly developed, inexpensive pesticide have shown it to be both environmentally safe and effective against the insects that have infected cotton crops.”

So cotton farmers will be able to use this new, cheap pesticide against the specific insects that are currently destroying the cotton crops. What does that mean?

Oh. It means that they’ll be able to produce more cotton. If you have more cotton on the market, there will no longer be a scarcity—in other words, the price is likely to drop. Yes, if I were a soybean farmer, this knowledge would definitely make me rethink my plan. Leave this choice in.

“(C) In the past several years there has been no sharp increase in the demand for cotton and for goods made out of cotton.”

This one is tempting! But it’s wrong anyway. :) I already know that there has been sufficient demand for cotton to raise the prices “dramatically.” The amount of cotton needed doesn’t have to increase for this to happen; all that needs to happen is that more people want to buy cotton than there is cotton available.

“(D) Many consumers consider cotton cloth a necessity rather than a luxury and would be willing to pay significantly higher prices for cotton goods than they currently pay.”

They’d be willing to pay even more for cotton than they already pay? In other words, there’s room for me to make even more money? Well then I should definitely switch to making cotton!

Oh, wait a minute. This choice strengthens the argument. I’m looking for a weaken, so this isn’t the right answer.

“(E) The species of insect that has infested cotton plants has never been known to attack soybean plants.”

That’s good if I stick with soybeans. But I’m planning to switch to cotton; if I do, then this won’t matter to me.

The correct answer is (B).

What did you learn on this problem? Come up with your own takeaways before you read mine below.

Key Takeaways for Weaken Problems:

(1) Know how to identify the question type. On CR, this usually means some form of the word weaken or a synonym such as undermine or call into question. The answer should be something that the makes the argument at least somewhat less likely to be valid.

(2) Lay out the premises and the conclusion so that you can think about the gap between them. The assumption “lives” in that gap—it’s something the author didn’t say but nevertheless must believe in order to get from the premises to the conclusion.

(3) Weaken questions will often try to trap us by putting in a strengthen answer. This problem did that twice! They’re also going to try to distract you with a choice that makes it sound like “Oh, maybe I don’t want to follow this plan, if that’s true”—except that the argument has already told you something else that makes what that choice says irrelevant (this is what answer C did).

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

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