How GMAT Data Sufficiency Works

Data Sufficiency is one of the GMAT’s longstanding and signature question types. It doesn’t ask you to solve a problem; it asks whether the problem could be solved with the information given. That one twist is arguably responsible for more confusion than any other question format on the GMAT. This guide covers the format, the five answer choices you’ll learn to love, the mindset shift that makes DS click, and the pitfalls that nearly every beginner falls into.

One housekeeping note before we start: Data Sufficiency now lives in the Data Insights section, not the quant section. If you learned the GMAT’s layout from an older prep book (or an aging coworker), that’s one of several things that changed in the November 2023 redesign, along with Sentence Correction disappearing entirely.

What a GMAT Data Sufficiency Question Looks Like

Every DS question has the same skeleton: a question, followed by two statements labeled (1) and (2). Your job is to decide whether the statements give you enough information to answer the question, alone or together.

The five answer choices are identical on every single DS question, and they always work like this:

• (A) Statement (1) ALONE is sufficient, but statement (2) alone is not.
• (B) Statement (2) ALONE is sufficient, but statement (1) alone is not.
• (C) BOTH statements TOGETHER are sufficient, but neither alone is.
• (D) EACH statement ALONE is sufficient.
• (E) The statements together are still NOT sufficient.

You’ll want these answer choices to become second nature so that you don’t have to read them every time you encounter a new DS question. We find that students are most successful when they hone a consistent, repeatable approach to these questions. Watch our tutors teach that approach in the video below.

The Mindset Shift: Sufficiency, Not Solutions

What makes DS feel alien at first is that you don’t actually need to solve the given problem to answer the question. You only need to know whether a single, unambiguous answer could be found.

Suppose that a question asks for the value of x, and statement (1) boils down to a single linear equation with one unknown. You don’t need to solve it. One linear equation, one unknown, exactly one value of x: that’s sufficient, and you don’t care what the numerical answer actually is. Just move on.

This is why strong “regular math” students sometimes struggle with DS at first: their instinct is to calculate everything, and DS cleverly punishes that instinct by draining your time. DS isn’t testing your ability to compute an answer. That’s what the Quantitative Reasoning section is for. It’s knowing when you have enough information to actually answer the question, and when you don’t.

How to Wash Your Brain: A Brief Guide

The most common self-inflicted wound on GMAT Data Sufficiency: letting statement (1) leak into your evaluation of statement (2).

The statements must be evaluated INDEPENDENTLY first. When you move to statement (2), you have to wipe statement (1) from your mind entirely, and after 90 seconds of working with statement (1), your brain does not want to let it go. 

If you catch yourself thinking “well, combined with what I already know…” while evaluating a lone statement, that’s contamination, and it usually shows up as a wrong answer, potentially on a very easy question. 

That’s why we advocate for “washing your brain” between evaluating answer choices. It’ll feel difficult at first, but with practice you’ll improve.

Only after each statement has been judged on its own do you consider them together, and only if neither was sufficient by itself.

This is, at its heart, the same skill we preach for GMAT Critical Reasoning: precision about what you actually know, versus what you’ve smuggled in from somewhere else.

Read DS Statements Like a Lawyer

DS statements are written with the same surgical precision as the rest of the exam, and as silly as it may sound, misreading causes far more DS errors than struggles with math or logic. If, for example, the question says “x is a positive integer” and you interpret it simply as “x is positive,” you’re almost certain to make a score-killing mistake, potentially on an easy question.=

It can be remarkably easy to miss a tiny detail on DS: the direction of a sign, or a phrase like “at most” or “distinct.” As unglamorous as it sounds, we strongly recommend reading every DS question twice before you even think about diving into the statements. It’s a small investment to ensure that you don’t slip up on a completely gettable question.

What Math Do You Need for GMAT Data Sufficiency?

Any quant topic that appears on the Quantitative Reasoning section is fair game on Data Sufficiency, including arithmetic, algebra, number properties, percentages, ratios, and statistics, among others. Nearly all Data Sufficiency questions are presented as word problems, so be prepared to do quite a bit of translation, regardless of the underlying math concepts. There’s no geometry on the current GMAT, and no calculus or trigonometry appears anywhere on the exam. 

An on-screen calculator is available throughout Data Insights, but on a well-designed DS question, it can waste your time instead of actually helping. If you find yourself calculating an exact value on a DS question, stop and ask whether you actually need to do the calculations. If you’re spending a lot of time clicking numbers on the on-screen calculator, you might be burning time unnecessarily.

Not all Data Sufficiency questions are math-based. Many questions are rooted solely in words and logic, and often feel like a variant on Critical Reasoning questions. 

How to Practice GMAT Data Sufficiency

If you’ve read any of our other guides, we’re going to sound like a broken record here: use official questions as much as possible for your practice, because “knockoff” questions often struggle to replicate the nuance that appears in actual, official DS questions.

If you run short on official DS questions, the good news is that you can always turn to an older edition of the GMAT Official Guides. Just be aware that pre-2023 guides included DS in the quant section, and you may encounter geometry-based questions: if you see those, skip them, because geometry is no longer on the GMAT.

How Many Data Sufficiency Questions Will You See on the GMAT?

According to the GMAT’s creators, Data Sufficiency questions make up 20-40% of the Data Insights section. That means that you’ll see 4-8 Data Sufficiency questions on the exam.