GMAT Data Sufficiency

The Data Sufficiency Section

Introduction

The GMAT test writers use the 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. As a result, if you find yourself doing much number crunching with the data sufficiency questions, you are doing something wrong.

Math Concepts You Should Know

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

The Answer Choices

The GMAT's 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 be immediately eliminated.

Similarly, if statement 2 is insufficient, then choices B and D can be immediately 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 These Questions

It seems a common mistake many test takers commit is to lack an exhaustive and analytical methodology to analyzing these questions. A simple tendency to overlook a step in the process 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 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 asked. To determine the area of a circle, you will need to know either the circle's diameter, radius, or circumference.

3.) Look at each of the two statements independently of each other.  Follow the process of elimination rules covered above when considering 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 tries to measure your ability to distinguish facts from careless assumptions. Do not rely on a visual assessment of a geometry question to determine angle sizes, parallel lines, etc. Finally, do not carry any information from one question to the next. You can count on seeing at least a few questions where a wrong selection is presented just 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 solve math problems.

Use process of elimination.  This GMAT section lends itself perfectly to process of elimination. If time becomes an issue, you can always look at the 2 statements in either order. Hence, if statement 1 is confusing, look at statement 2 to 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 your choices are D or E. A favorite of the GMAT testers is to use 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.  The test makers will not try to trick you in this way with these questions. However, you must assume in certain abstract questions such as "What is the value of x?" that x can be a fraction and/or a negative number.

Practice, practice, practice.  If you spend some time practicing these questions, you will be able to internalize these tips and strategies. You will also become very comfortable with the questions from this portion of the test and will quickly realize if there are any math areas such as geometry or algebra where you will need to brush up on your skills. When it comes time to sit for the GMAT, you will want to know the important data relationships for the various math areas tested.

Data sufficiency practice questions

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