How to Avoid the C Trap in GMAT Data Sufficiency Questions

by Target Test Prep, Nov 21, 2022

Data Sufficiency (DS) questions in the GMAT Quant section are known for their ability to twist your brain and challenge both your math and data analysis skills. One of the most challenging types of DS math questions, the so-called C trap lulls test-takers into a false sense of security because it appears to be easy and straightforward. This article provides examples of C-trap questions in DS, as well as ways to identify and work through these tricky problems.

What Is a Data Sufficiency Question?

A GMAT Data Sufficiency question contains a question stem and two statements (statement one and statement two). We need to use the information provided in those statements to determine whether we are able to answer the question posed in the stem.

What makes GMAT Data Sufficiency questions so different from Problem Solving questions is that, whereas in Problem Solving questions, you need to determine a numerical answer, in DS questions, you need only to determine sufficiency. In other words, you need to determine whether the information provided is sufficient to answer the question. However, you do so without having to calculate that answer.

Because you do not have to do the math “in full” for most Data Sufficiency problems, the GMAT-makers sometimes try to trick or bait you into selecting a particularly attractive answer. This is referred to as a trap. The trap we will discuss in this article is the “C trap.”

So, let’s talk about what exactly a C trap question is.

What Exactly Is a C Trap?

In any Data Sufficiency question, we are always provided with the same 5 answer choices:

A) Statement one alone is sufficient.

B) Statement two alone is sufficient.

C) Both statements together are sufficient, but neither statement alone is sufficient.

D) Either statement alone is sufficient.

E) Statements one and two together are insufficient.

As we see above, we select answer choice C when both statements together are sufficient to answer the question. The essence of any C trap is that C appears to OBVIOUSLY be the correct answer when, in fact, it is not. Thus, we need to be very careful not to quickly rush through the statements and hastily select C when analyzing DS questions.

Aside from taking your time and being in the moment, a good way to stop yourself from making hasty choices is to understand the mathematical reasoning behind the C trap. In one very common example of the C trap, the reasoning is that you can sometimes have two variables and only one equation, but you can still determine unique values for those variables. The fact is you likely did not learn this in a middle school or high school algebra class. However, it’s something you certainly need to know for the GMAT. So, let’s discuss this important point further.

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