GMAT · Section guide 5 · 5 min read

GMAT Data Sufficiency: how it works and how to approach it

How GMAT Data Sufficiency questions work in Data Insights: the five fixed answer options, a step-by-step method, common traps and original examples.

What makes Data Sufficiency different

Data Sufficiency (DS) is unlike any other question on the GMAT. You are not asked to find an answer. You are asked whether the information given is enough to find one.

Each DS question has:

• a question, which may ask for a value ("What is x?") or a yes/no answer ("Is x greater than 5?");
• two statements, labeled (1) and (2), each giving extra information.

You decide whether the question can be answered using the statements, and choose from five fixed options that are the same on every DS question.

In the Focus Edition, DS sits in the Data Insights section. It can be quantitative, but it can also be verbal or logical, for example about schedules, rankings or business rules.

The five answer options

In our own words, the five options are:

Learn these so well that you never need to read them on test day. Many test takers remember the order as "1 alone, 2 alone, together, each, neither".

What "sufficient" means

A statement is sufficient if it lets you reach exactly one answer to the question.

• For a value question, sufficient means one single value. If x could be 3 or −3, that is not sufficient.
• For a yes/no question, sufficient means a definite answer, either always yes or always no. A definite no is sufficient. If the answer is sometimes yes and sometimes no, it is not sufficient.

You never need to calculate the final number. Once you know that only one answer is possible, you can stop.

A step-by-step method

1. Understand the question. Simplify it if you can. "Is 2*x* + 4 > 10?" is the same as "Is x > 3?"
2. Evaluate statement (1) alone. Forget statement (2). Is (1) sufficient?
3. Evaluate statement (2) alone. Forget statement (1) completely. Is (2) sufficient?
4. If neither is sufficient alone, combine them.
5. Choose the option that matches.

A useful elimination pattern:

• If (1) is sufficient, the answer is A or D.
• If (1) is not sufficient, the answer is B, C or E.

Examples of our own

A value question. What is the value of x? (1) 3*x* + 2 = 17. (2) x² = 25.

• Statement (1) gives x = 5: one value, sufficient.
• Statement (2) gives x = 5 or x = −5: two values, not sufficient.
• Answer: A.

A yes/no question. Is the integer n even? (1) 3*n* is even. (2) n + 4 is even.

• Statement (1): if 3*n* is even, n must be even, because an odd number times 3 is odd. Definite yes: sufficient.
• Statement (2): if n + 4 is even, n must be even. Definite yes: sufficient.
• Answer: D.

A verbal DS question. Did Priya arrive at the meeting before Tom? (1) Priya arrived before Sam. (2) Sam arrived before Tom.

• Statement (1) alone says nothing about Tom: not sufficient.
• Statement (2) alone says nothing about Priya: not sufficient.
• Together: Priya before Sam, and Sam before Tom, so Priya arrived before Tom. Sufficient.
• Answer: C.

Common traps

• Carrying information across. When you judge statement (2) alone, you must forget statement (1). This is the most common DS error.
• Assuming integers or positives. Unless the question says so, a variable may be negative, zero or a fraction. Test those cases.
• Solving when you don't need to. You only need to know whether one answer exists, not what it is.
• Choosing C too quickly. Before combining, make sure that neither statement is sufficient on its own.
• Missing that "no" is an answer. A statement that always gives "no" is sufficient.

Testing cases

For yes/no questions, a strong technique is to test values. Try to find one case where the answer is yes and another, still meeting the statement, where the answer is no. If you can find both, the statement is not sufficient. Use a variety of cases: positive and negative, whole numbers and fractions, zero, large and small values.

Exam tip: write "AD / BCE" on your notepad at the start of each DS question and cross out options as you go. It keeps your logic visible and stops you mixing up the statements.

How to practice

Start with untimed sets, writing out your reasoning for each statement separately. Then move to timed mixed Data Insights sets. When you review a missed question, ask which of the traps above caught you. Most DS mistakes come from the same few habits, and fixing them brings steady gains.

Check yourself

1. What does "sufficient" mean for a value question? For a yes/no question?
2. If statement (1) alone is sufficient, which two answers are still possible?
3. Why must you ignore statement (1) when evaluating statement (2)?
4. Is a statement that always gives the answer "no" sufficient?

Find practice material and the rest of this series on the GMAT hub.