Wrong answers in Critical Reasoning -Out of Scope-

By Clipper Ledgard

Critical Reasoning questions in the GMAT are well thought and, in many cases, challenging. Nevertheless, eliminating wrong answers may not be as difficult as it seems if we use the right approach.

While the questions are cleverly created, the explanations in the official guide can be confusing and could clearly be improved.

For example, the question below is taken from the Official Guide 2018.

Many industrialized nations are trying to reduce atmospheric concentrations of carbon dioxide, a gas released by the burning of fossil fuels. One proposal is to replace conventional cement, which is made with calcium carbonate, by a new “eco-cement.” This new cement, made with magnesium carbonate, absorbs large amounts of carbon dioxide when exposed to the atmosphere. Therefore, using eco-cement for new concrete building projects will significantly help reduce atmospheric concentrations of carbon dioxide.

Which of the following, if true, most strengthens the argument?

1. The cost of magnesium carbonate, currently greater than the cost of calcium carbonate, probably will fall as more magnesium carbonate is used in cement manufacture.
2. Eco-cement is strengthened when absorbed carbon dioxide reacts with the cement.
3. Before the development of eco-cement, magnesium-based cement was considered too susceptible to water erosion to be of practical use.
4. The manufacture of eco-cement uses considerably less fossil fuel per unit of cement than the manufacture of conventional cement does.
5. Most building-industry groups are unaware of the development or availability of eco-cement.

Official Guide approach

The Guide eliminates the wrong answers the following way:

Situation

Many nations are trying to reduce atmospheric concentrations of carbon dioxide. One proposed method is to use a new type of “eco cement” that absorbs carbon dioxide from air.

Reasoning

What evidence, combined with the cited facts, would most support the prediction that using eco cement will significantly help reduce atmospheric concentrations of carbon dioxide? The prediction assumes that the use of eco cement would be an effective way to reduce carbon dioxide levels. Any evidence supporting this assumption will support the prediction.

1. Since eco cement uses magnesium carbonate, the prediction that magnesium carbonate prices will fall suggests that a potential financial barrier to widespread eco cement use will diminish. However, those prices may not fall enough to make eco cement cost competitive with regular cement.
2. Even if absorbed carbon dioxide strengthens eco cement, the strengthened eco cement might still be much weaker than regular cement and thus might never become widely used, in which case it will not significantly help reduce atmospheric concentrations of carbon dioxide.
3. Even if eco cement is less susceptible to water erosion than earlier forms of magnesium based cement were, it might still be much more susceptible to water erosion than regular cement is, and thus might never become widely used.
4. Correct. This suggests that manufacturing eco cement produces much less carbon dioxide than manufacturing regular cement does, so it supports the claim that widespread use of eco cement would be an effective way to reduce carbon dioxide levels.
5. If anything, this lack of awareness makes it less likely that eco cement will become widely used, which in turn makes it less likely that eco cement will significantly help reduce atmospheric concentrations of carbon dioxide.

The correct answer is D.

The explanations are correct, but long; we must pay close attention to follow the reasoning. In addition, these explanations will not help us very much if we want to improve our skills.

Another approach

In many cases, as in this question, the best and fastest approach could be the elimination of wrong answer choices because they are out of scope -the most common wrong answers. To apply this strategy, we must identify the scope. How do we do this? Believe it or not, by simply looking at the conclusion. I have already written about the conclusion in a previous post:  The Importance of the Conclusion in Critical Reasoning.

So, look at the stimulus and identify the conclusion:

Many industrialized nations are trying to reduce atmospheric concentrations of carbon dioxide, a gas released by the burning of fossil fuels. One proposal is to replace conventional cement, which is made with calcium carbonate, by a new “eco-cement.” This new cement, made with magnesium carbonate, absorbs large amounts of carbon dioxide when exposed to the atmosphere. Therefore, using eco-cement for new concrete building projects will significantly help reduce atmospheric concentrations of carbon dioxide.

Once we have identified the conclusion, it is easy to spot the scope: the reduction of the atmospheric concentrations of carbon dioxide. The key words are reduction and carbon dioxide. Notice that the price – choice A, – the strength of the cement – choice B, – susceptibility to water erosion or practical use – choice C, – and awareness of the development or availability of eco-cement – choice E, –  are irrelevant to the conclusion; none of these choices deals with the reduction of carbon dioxide.

Choice D, however, uses additional information to support the conclusion: the manufacture of eco-cement uses considerably less fossil fuel per unit of cement than the manufacture of conventional cement does.

In short, we can approach many critical reasoning questions just by focusing on the scope of the argument, thus we can avoid spending too long to answer a question.