GMAT · Guides · October 22, 2026 · 10 min read

GMAT Data Sufficiency: the five answers, the AD/BCE method, traps and worked examples

Data Sufficiency (DS) is a question type in the GMAT Data Insights section. You get a question and two statements, and you do not have to answer the question: you decide whether the information is enough to answer it. Every DS question has the same five answer choices, so once you know them by heart and eliminate them in a fixed order (the AD/BCE method), DS becomes one of the most predictable formats on the test.

What a Data Sufficiency question looks like

A DS question has three parts: a question stem (sometimes with extra facts), statement (1) and statement (2). The two statements are always true. Your task is to judge whether each statement, alone or together with the other, gives exactly one answer to the question.

Data Insights has 20 questions in 45 minutes and a basic on-screen calculator. GMAC does not publish the mix, but test-takers usually report five or six DS questions. DS can test maths (algebra, numbers, rates, statistics) or plain-English logic; geometry is no longer tested. See the GMAT syllabus and exam pattern for the full section breakdown.

The five answer choices (they never change)

Learn them by heart: A = only (1), B = only (2), C = only together, D = each alone, E = not even together.

The AD/BCE method

Do not look at both statements at once. Start with statement (1) on its own:

• If (1) is sufficient, the answer can only be A or D. Now check (2) alone: sufficient means D, not sufficient means A.
• If (1) is not sufficient, the answer is B, C or E. Check (2) alone: sufficient means B. If (2) is also not sufficient, combine them: sufficient together means C, not sufficient means E.

This order keeps the statements apart, and if you get stuck halfway you have already cut the choices to two or three. The GMAT penalises unanswered questions, so an informed guess always beats a blank.

Value questions and yes/no questions

There are two kinds of DS question, and “sufficient” means something slightly different in each.

• Value questions ask for a number: “What is the value of x + y?” A statement is sufficient only if it leads to one value. Two possible values means not sufficient.
• Yes/no questions ask whether something is true: “Is x > 5?” A statement is sufficient if it leads to an answer that is always yes or always no. If some allowed numbers give yes and others give no, it is not sufficient.

If a value question asks for x + y, you need the sum, not x and y separately (worked example 1 shows why this matters).

A definite “no” is sufficient

This is the rule that catches the most people. In a yes/no question, a statement that proves the answer is “no” is just as sufficient as one that proves “yes”. Here is an original logical DS question from our bank (ds-0234):

A software company releases an update only after the update has passed both a security review and a performance test. Has the company released update 4.2?

(1) Update 4.2 has not passed the performance test.

(2) Update 4.2 has passed the security review.

Statement (1): the update failed one of the two required checks, so it cannot have been released. The answer is a certain “no”, so (1) is sufficient. Statement (2): passing the security review is necessary but not enough; the update may or may not have passed the performance test. Not sufficient. The answer is A. Test takers who feel that “no” is not an answer pick E here.

Testing cases: negatives, zero and fractions

When algebra does not settle a statement, plug in numbers and try to break it: look for one allowed number that gives yes and another that gives no. If you find both, the statement is not sufficient. Check these cases whenever the question does not restrict the variables:

• Negative numbers. x² > 25 is true for x = 6 and for x = −6.
• Zero. Zero is even, it is neither positive nor negative, and 0 × anything = 0.
• Fractions between −1 and 1. For 0 < x < 1, x² is smaller than x; for −1 < x < 0, x³ is greater than x.
• Equal values. Can x and y be the same number? Can two primes be equal?
• Integers only if stated. “x is a number” includes 2.5 and −1/2. Only assume integers when the question says so.

The most common Data Sufficiency traps

1. One tested case. x = 2 works, so you call the statement sufficient. One example proves nothing; one counterexample proves “not sufficient”. Always try a deliberately different second case.
2. Carry-over. Judging (2) alone while still using what (1) told you. Mentally cover (1) first; combining comes only at the C/E step.
3. Solving instead of judging. DS asks only whether an answer exists. If two independent linear equations fix two unknowns, stop: you do not need the numbers.
4. Treating “no” as insufficient. See the section above.
5. Picking C too quickly. Together feels safe, but often one statement alone already does the job.
6. Forgetting the stem. Facts in the question stem (for example “k is a positive integer”) apply to both statements.

Logical (non-math) Data Sufficiency

Some DS questions have almost no arithmetic: rankings, schedules, eligibility rules. The method is identical. Two habits help:

• Translate rules into arrows. “Released only after passing both checks” means released → passed both. “Free delivery if, and only if, the order is over $40 or the customer has a card” means either condition alone is enough.
• Read “or” and “and” literally. Example from our bank (ds-0127): a shop delivers free “if, and only if, the order totals more than $40 or the customer holds a loyalty card. Was Priya’s order delivered free of charge? (1) Priya’s order totaled $35. (2) Priya holds a loyalty card.” Statement (1) fails one condition but leaves the card open, so not sufficient. Statement (2) meets a condition, so delivery was free: sufficient. Answer B. Reading “or” as “and” leads people to A or C.

Four worked examples, from easy to hard

All four are original questions from the Nomto bank. Try each one before reading the solution.

Example 1 (easy, value question)

What is the value of x + y?

(1) x − y = 3

(2) 2x + 2y = 18

Statement (1). It gives the difference, not the sum. x = 3, y = 0 gives x + y = 3; x = 5, y = 2 gives 7. Two values: not sufficient. The answer is B, C or E.

Statement (2). Divide by 2: x + y = 9. One value: sufficient.

Answer: B. The trap is C: thinking you need x and y separately and therefore both equations. The question asks only for the sum, and statement (2) gives it directly.

Example 2 (yes/no question, negatives)

Is x > 5?

(1) x² > 25

(2) 3x − 7 > 11

Statement (1). x² > 25 means x > 5 or x < −5. x = 6 gives yes; x = −6 gives no. Not sufficient.

Statement (2). 3x > 18, so x > 6, and every such x is greater than 5. Always yes: sufficient.

Answer: B. The trap is taking the square root in (1) and keeping only x > 5. Negative numbers such as −6 also have squares greater than 25, which is why D is wrong.

Example 3 (inequalities, the sign of a variable)

Is x > y?

(1) x/y > 1

(2) x + y > 0

Statement (1). x/y > 1 means x and y have the same sign and x is further from zero. x = 4, y = 2: yes. x = −4, y = −2: no (−4 is less than −2). Not sufficient.

Statement (2). x = 3, y = 1: yes. x = 1, y = 3: no. Not sufficient.

Together. If both were negative, x + y would be negative, which (2) rules out. So both are positive, and multiplying x/y > 1 by the positive y gives x > y. Always yes: sufficient.

Answer: C. The trap is A: multiplying (1) by y without checking its sign. You can multiply an inequality by a variable only when you know whether it is positive or negative.

Example 4 (hard, fractions)

If x ≠ 0, is x⁴ > x²?

(1) x³ > x

(2) x⁵ > x³

Rephrase first. x² is positive, so divide both sides by it: the question is whether x² > 1, that is, whether x > 1 or x < −1.

Statement (1). x³ > x means x(x² − 1) > 0, which holds when x > 1 or when −1 < x < 0. x = 2 gives yes. x = −1/2 gives x⁴ = 1/16 and x² = 1/4, so x⁴ is not greater: no. Not sufficient.

Statement (2). x⁵ > x³ means x³(x² − 1) > 0. x³ has the same sign as x, so this holds in exactly the same two ranges as (1). Not sufficient.

Together. The two statements describe the same set of numbers, so combining them adds nothing; x = 2 and x = −1/2 still both fit. Not sufficient.

Answer: E. The trap is D. If you test only integers, both statements seem to force x > 1. The negative fractions between −1 and 0 are the case that breaks them.

Practice set: three more questions

Use the AD/BCE order and note your answer before checking.

Question 1. If p and q are prime numbers, what is the value of p?

(1) p + q = 15

(2) p − q = 11

Question 2. Working together at their respective constant rates, machines A and B fill an order in 6 hours. How many hours would machine A, working alone at its constant rate, take to fill the order?

(1) Machine B, working alone at its constant rate, would take 15 hours to fill the order.

(2) Machine A’s rate is 1.5 times machine B’s rate.

Question 3. Pumps X and Y each work at a constant rate. Working alone, can pump X fill an empty tank in less than 6 hours?

(1) Working together, pumps X and Y can fill the empty tank in 4 hours.

(2) Pump X works at a faster rate than pump Y.

Answers

Question 1: B. The only even prime is 2. In (1), an odd sum of two primes forces one of them to be 2, so the pair is 2 and 13, but either can be p: p = 2 or p = 13, not sufficient. In (2), if q were odd, p = q + 11 would be even and greater than 2, so not prime. Hence q = 2 and p = 13: sufficient. The trap is finding p = 13 in (1) and forgetting that the primes can swap places.

Question 2: D. Rates add: together A and B do 1/6 of the order per hour. (1) B’s rate is 1/15, so A’s rate is 1/6 − 1/15 = 1/10: A takes 10 hours, sufficient. (2) A’s rate is 1.5r and B’s is r, so 2.5r = 1/6, r = 1/15 and A’s rate is 1/10: again 10 hours, sufficient. The trap is thinking a ratio of rates cannot give an actual time; combined with the 6-hour total, it can.

Question 3: E. (1) The rates add up to 1/4 tank per hour, but X could take 5 hours (Y 20 hours, yes) or 12 hours (Y 6 hours, no): not sufficient. (2) Faster than Y says nothing about X’s actual time: not sufficient. Together, X supplies more than half of the joint rate, so its time is between 4 and 8 hours: 5 hours gives yes, 7 hours (Y about 9.3 hours) gives no. Not sufficient. The trap is C: “faster than Y, so well under 6 hours”.

How to get faster at Data Sufficiency

• Budget under two minutes. Data Insights allows a little over two minutes per question, and DS should be quicker than the multi-part formats.
• Rephrase the question first. “Is x⁴ > x²?” becomes “Is |x| > 1?”; “Is k divisible by 15?” becomes “Is k divisible by 3 and by 5?”.
• Write AD/BCE on your noteboard and cross letters out as you go.
• Log your errors by trap. If most misses are “one tested case”, the fix is a habit (always try a negative and a fraction), not more theory.

For the other half of the logic skills the GMAT tests, see our guide to GMAT Critical Reasoning. To see DS next to every other question format, go to GMAT sample questions. GMAC’s free official practice exams on mba.com are the best way to try DS under real timing.