GMAT Data Sufficiency—The Great Equalizer

When students come to me for help on the Quant section of the GMAT™ exam, they often possess exceptional math skills, sometimes way more advanced than my own. Their inability to reach a high score on the GMAT Quant section usually relates to one simple mistake: they are treating the GMAT like a math test, when it is really a “Quantitative Reasoning” test.

When I go through a few Official GMAT Practice Test questions with these students to see what categories of questions they are missing, it is always the same story:

• If the problem is a pure math question (not that common on the exam), then they find the correct answer quickly and easily.
• If it is a complicated Data Sufficiency question assessing critical thinking and hypervigilance, or an abstract problem-solving question in which most of the difficulty comes from obtuse or clever wording, they miss it.

What is the GMAT Quant section really testing?

Repeat news flash: the GMAT is a reasoning test, not a math content test!

The underlying math used to create GMAT Quant problems is not particularly complex or challenging, but the questions can be difficult. As I always joke in my classes, GMAT question writers can literally turn “What is 1 + 1?” into a 90^th percentile question using a variety of mechanisms.

When you are preparing for the GMAT Quantitative Reasoning section, you need to first fill in any knowledge gaps and then develop a high level of fluency with the most tested content. Once you get to that point, however, you must learn how to deal with the more sinister difficulty lurking in these questions if you want to find the correct answer.

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Business schools want critical thinkers, creative problem-solvers, good decision makers—people who can take core quant knowledge and solve a unique GMAT Quant question using that information. Given this, GMAT question writers need to make the Quant section of the exam in such a way that it assesses not just who has the requisite quant knowledge, but also who has these more important skills and abilities.

How does Data Sufficiency go beyond pure math?

GMAT Data Sufficiency is GMAC’s number-one tool for “equalizing” the playing field on the Quant section and making it more of a reasoning test. It is an amazingly sophisticated tool for assessing three things:

• Who is highly critical and always questioning given information?  
• Who leverages every little piece of information to make the best decision possible?
• Who can recognize the “con” and select a correct answer that differentiates them from other very smart people? 

Essentially, Data Sufficiency questions are designed to elicit very particular mistakes related to the skills above. When these mistakes are made, they usually relate to some mathematical concept, but they are often more related to particular “cons” that make you under- or over-leverage information. In our curriculum, we present a set of more sophisticated strategies for dealing with these cons, but following the important set of best practices below helps you avoid many common mistakes.

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GMAT Data Sufficiency best practices

Understand the rules of the game in Data Sufficiency.

Be clear on what it really means for a statement to be sufficient in a “yes/no” or “what is the value?” question; know the answer choices without thinking; don’t carry information between statements.

Do not go to the statements until you understand the question and organize all the given information.

In difficult GMAT data sufficiency questions, the most important information is almost always hidden in the question stem, not the statements.

Always be critical and always leverage harder.

There are only two mistakes you can make in a GMAT Data Sufficiency question: either you under- or over-leverage the given information. For every statement that you analyze in a data sufficiency question, make sure you are leveraging all available data and be careful that you are not making assumptions. Find the surprisingly sufficient piece of information or the hard-to-recognize contrarian example that makes a statement insufficient.

Make sure your answer is really differentiating you from other smart people.

If something is too good to be true in Data Sufficiency, it usually is. Use the hints within different Data Sufficiency constructs to help prove sufficiency or insufficiency.

Sample GMAT Data Sufficiency question

To show these best practices in action, let’s determine the correct answer to a full official problem. First try this sample question on your own:

The participants in a race consisted of 3 teams with 3 runners on each team. A team was awarded 6 – n points if one of its runners finished in nth place, where 1 ≤ n ≤ 5. If all of the runners finished the race and if there were no ties, was each team awarded at least one point?  

(1) No team was awarded more than a total of 6 points.

(2) No pair of teammates finished in consecutive places among the top five places. 

1. Statement (1) ALONE is sufficient but statement (2) ALONE is not sufficient. 
2. Statement (2) ALONE is sufficient but statement (1) ALONE is not sufficient. 
3. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. 
4. EACH statement ALONE is sufficient. 
5. Statements (1) and (2) TOGETHER are not sufficient. 

As is typical in many GMAT Data Sufficiency questions, all of the important information is abstractly presented in the question stem. It is also worth pointing out that this problem has very little to do with math: it is assessing whether you can read carefully and follow every instruction and restriction presented in the problem.

Assessing the question stem

Before moving to the statements, you should summarize all the given information and figure out the exact goal of the question. This starts with determining how many total points are available in this race.

According to the given instructions:

• 5 points go to 1^st place
• 4 points go to 2^nd place
• 3 points go to 3^rd place
• 2 points go to 4^th place
• 1 point goes to 5^th place

This means there are 15 total points that get distributed. The goal is to determine definitively whether each team got at least one point (or not). Make sure to note that all runners finished and there were no ties—if you are told something like this, it usually matters.

Assessing statement (1)

You can see that the upper limit of 6 guarantees that each team must have received at least one point. There is no way to get to a total of 15 without each team contributing some points to the total—that is, 2 teams x 6 points can’t get you to 15.

Since this statement is quite clearly sufficient on its own, you know the answer must be (A) or (D) and you need to then carefully analyze the other statement (when one statement is easy, the other is usually quite tricky!).

Assessing statement (2)

This one takes more time to assess and feels like it might be cleverly sufficient at first glance. However, by considering a few cases that meet this condition, you can prove that the statement is definitively NOT sufficient:

In Data Sufficiency, it is relatively easy to prove insufficiency, but much harder to prove sufficiency. Here you can show definitively that you can get both a yes and a no answer, so you are sure that statement 2 is not sufficient. As a result, the correct answer is (A). 

A few parting thoughts on this question and GMAT Data Sufficiency questions overall:

• Consider carefully why certain restrictions are given. For instance, if it says x is a non-negative integer, I’ll bet you $1000 that zero matters in the question! (Otherwise, they would just say x is positive.)
• If you are not finding some dopamine response with your answer in which you suddenly “get it,” leverage harder or be more critical…you need to find something clever in the problem if it is going to differentiate you at the far end of the curve. For example, if it is easy to solve the problem using both statements, the answer will not be (C)… leverage each statement harder!

When you master all the components of GMAT Data Sufficiency and learn how to play the game cleverly, you are able to outperform people with equivalent or even superior Quant knowledge and increase your Quant score dramatically.

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