The Data Sufficiency Section

Introduction

GMAT test writers use data sufficiency questions to test your ability to "reason quantitatively." This stands in sharp contrast to the problem solving section, which is designed to test how well you manipulate numbers. If you find yourself doing a lot of number crunching on the data sufficiency questions, you are doing something wrong.

Math Concepts You Should Know

The data sufficiency questions cover math that nearly any college-bound high school student will know. In addition to basic arithmetic, you can expect questions testing your knowledge of averages, fractions, decimals, algebra, factoring, and basic principles of geometry such as triangles, circles, and how to determine the areas and volumes of simple geometric shapes.

The Answer Choices

GMAT data sufficiency questions will all have the exact same answer choices. Memorize these answer choices before you take the exam. It will help you better utilize your time in the quantitative section. The answer choices are summarized below as you will see them on the GMAT exam.

1. Statement 1 alone is sufficient but statement 2 alone is not sufficient to answer the question asked.
2. Statement 2 alone is sufficient but statement 1 alone is not sufficient to answer the question asked.
3. Both statements 1 and 2 together are sufficient to answer the question but neither statement is sufficient alone.
4. Each statement alone is sufficient to answer the question.
5. Statements 1 and 2 are not sufficient to answer the question asked and additional data is needed to answer the statements.

Use Process of Elimination

If statement 1 is insufficient, then choices A and D can immediately be eliminated.

Similarly, if statement 2 is insufficient, then choices B and D can immediately be eliminated.

If either statement 1 or 2 is sufficient on its own, then choices C and E can be eliminated.

A Simple 4 Step Process for Answering These Questions

Many test takers make the mistake of not arming themselves with a systematic method for analyzing the answer choices for these questions. Overlooking even one step in the process outlined below can make a big difference in the final quantitative score you will be reporting to your selected business schools.

1.) Study the questions carefully.  The questions generally ask for one of 3 things: 1) a specific value, 2) a range of numbers, or 3) a true/false value. Make sure you know what the question is asking.

2.) Determine what information is needed to solve the problem.  This will, obviously, vary depending on what type of question is being asked. For example, to determine the area of a circle, you need to know the circle's diameter, radius, or circumference. Whether or not statements 1 and/or 2 provide that information will determine which answer you choose for a data sufficiency question about the area of a circle.

3.) Look at each of the two statements independently of the other.  Follow the process of elimination rules covered above to consider each statement individually.

4.) If step 3 did not produce an answer, then combine the two statements.  If the two statements combined can answer the question, then the answer choice is C. Otherwise, E.

Data Sufficiency Tips and Strategies

Use only the information given in the questions.  The GMAT CAT seeks to measure your ability to distinguish facts from careless assumptions. Do not rely on a visual assessment of a diagram accompanying a geometry question to determine angle sizes, parallel lines, etc. In addition, do not carry any information over from one question to the next. Each question in the data sufficiency section of the GMAT stands on its own. You can count on seeing at least a few questions where a wrong answer choice tries to capitalize on this common fallacy.

Do not get bogged down with complicated or lengthy calculations.  As we stated before, these questions are designed to test your ability to think conceptually, not to solve math problems.

Use process of elimination.  This GMAT section lends itself perfectly to using the process of elimination. If time becomes an issue, you can always look at the 2 statements in either order. Remember, the order you analyze the two statements in doesn't matter, so long as you begin by looking at them individually. If you find statement 1 confusing, you can save time by skipping to statement 2 and seeing whether it can help you eliminate incorrect answer choices.

Be on the lookout for statements that tell you the same thing in different words.  When the 2 statements convey the same exact information, you will know, through process of elimination, that the correct answer choice is either D or E. A favorite ploy of GMAT testers is to mix ratios and percentages. Here is an example where Statement 2 simply states backwards the exact same information provided by Statement 1.

1. x is 50% of y
2. the ratio of y:x is 2:1 

Make real-world assumptions where necessary.  You must assume that, in certain abstract questions such as "What is the value of x?", that x might be a fraction and/or a negative number.

Practice, practice, practice.  The more time you spend practicing data sufficiency questions, the better able you will be to internalize the tips and strategies given above. You will also become very comfortable with the type of questions from this portion of the test, and will quickly realize if there are any math areas, such as geometry or algebra where you need to brush up your skills. When it comes time to sit for the GMAT, you will want to know key math formulas and data relationships off the top of your head.

Click here to see our data sufficiency practice questions.

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