GRE® Quantitative Comparison: A Strategy Guide
If you've started practicing for the GRE® Quant section, you've probably met Quantitative Comparison questions.
They give you two quantities — Quantity A and Quantity B — and ask which is bigger. Or whether they're equal. Or whether you can't tell.
They look simple. Sometimes they are. But something about the format trips up a lot of test takers. You read the question, do some math, compare the quantities, pick an answer. Then you check the key and find out you were wrong.
Not because you didn't know the math. Because the format nudges you into assumptions you don't notice in the moment. Or you calculated something you didn't need to calculate. Or you forgot that the answer choice "can't be determined" even existed.
That experience is common. And it points to something important: QC questions aren't just math problems. They're reasoning problems that happen to use math. The distinction matters more than almost anything else about this question type.
We're going to walk through how QC works on the GRE®, the approach that tends to produce the best results, and the traps that catch even strong math students.
What Quantitative Comparison Looks Like on the GRE®
Before getting into strategy, it helps to understand the format.
The Structure
Every QC question presents two quantities. Quantity A is on the left. Quantity B is on the right. Below them, you get the same four answer choices every time:
(A) Quantity A is greater.
(B) Quantity B is greater.
(C) The two quantities are equal.
(D) The relationship cannot be determined from the information given.
You pick one. There's no partial credit. There's no combination of answers.
Some questions include additional information above the quantities — a centered statement that applies to both. It might give you the value of a variable, or a geometric figure, or a condition like "x is a positive integer."
That centered information is part of the question. It constrains what the variables can be. Ignoring it — or forgetting it — is one of the most common reasons test takers get QC questions wrong.
How Many QC Questions
QC questions make up roughly 40 percent of the GRE® Quant section. The Quant section has two parts — the first with 12 questions and the second with 15. Across both, you can expect about 11 to 14 QC questions.
That's a significant chunk of your Quant score. If you're strong at standard math problems but weak at QC, your score will reflect it. Getting comfortable with the format is one of the highest-leverage things you can do for your Quant score.
The Core Approach: Reason, Don't Calculate
Most people approach QC questions the same way they approach standard math problems — calculate both quantities, then compare the results.
That approach works when the quantities are specific numbers. If Quantity A is
But a lot of QC questions involve variables. And when variables are involved, calculating both sides is often the wrong approach.
The reason: variables can take different values. The relationship between Quantity A and Quantity B might depend on what the variable is. If you pick one value and calculate, you find the relationship for that value — but you don't know if the relationship holds for other values.
The approach that tends to work better:
- Look at what's given and what's not.
- Simplify both quantities if you can.
- Test specific values — including edge cases.
- Determine whether the relationship is consistent or depends on the variable's value.
This approach gets you to the answer through reasoning, not calculation. It's faster, and it catches the cases where the answer is (D).
Think of it like a trial in court. You don't need to prove Quantity A is greater in every possible scenario. You need to figure out whether it's always greater, always equal, or whether it depends. Testing a few well-chosen values is usually enough to find out.
The Four Answer Choices
Understanding what each answer choice means — and what it doesn't mean — is the foundation of QC strategy.
(A) Quantity A is greater
This means Quantity A is greater than Quantity B for every value that satisfies the given information. Not just for the value you tested. For every valid value.
If you test one value and Quantity A is greater, that doesn't mean (A) is the answer. You need to check whether it's always greater. If there's a value where Quantity B is greater or where they're equal, the answer isn't (A).
(B) Quantity B is greater
Same logic. Quantity B is greater for every valid value of the variables.
(C) The two quantities are equal
The quantities are equal for every valid value. Not just for one value you picked — for all of them.
(D) The relationship cannot be determined
This means the relationship depends on what the variable's value is. For some values, Quantity A is greater. For others, Quantity B is greater. Or for some values they're equal and for others they're not.
(D) is the answer when the relationship isn't consistent. It's also the answer when you don't have enough information to determine the relationship at all.
Here's the key thing about (D): it's an answer choice, not a fallback. A lot of test takers treat (D) as a shrug — "not sure." It's not. It's a specific claim: the relationship can't be determined from the information given. If the relationship can be determined — even if it takes some work — the answer isn't (D).
Strategy 1: Test Edge Cases
When a QC question involves variables, the relationship might depend on what the variable is. The fastest way to find out is to test specific values.
But not just any values. Edge cases.
Edge cases are the values that tend to break assumptions. The ones that behave differently from positive integers. On the GRE®, the edge cases that matter most are:
- Zero
- Negative numbers
- Fractions between 0 and 1
- Fractions between -1 and 0
- One
- Numbers greater than 1
Here's how it works. Test a "normal" value first — say, 2 or 5. Note the relationship. Then test an edge case — 0, or a negative, or a fraction. If the relationship changes, the answer is (D).
Example:
Quantity A:
x^2 Quantity B:
x No additional information.
Test
Test
The relationship changed. The answer is (D).
Testing edge cases is the single most powerful QC strategy. Most (D) answers exist because a variable could be zero, negative, or a fraction. If you only test positive integers, you may miss those cases and pick the wrong answer.
Strategy 2: Simplify Before Comparing
Sometimes both quantities look different but simplify to the same thing. Before you start testing values, try to simplify both sides.
Example:
Quantity A:
3(x + 2) - 3x Quantity B:
6
If you start testing values, you'd plug in numbers for x and compare. But simplify Quantity A first:
Quantity A simplifies to 6. Quantity B is 6. The answer is (C), and you didn't need to test a single value.
Simplification works because QC questions are often designed to look more complex than they are. The test writers build in a simplification that makes the comparison obvious. If you simplify before comparing, you find the shortcut.
Common simplification moves:
- Distribute and combine like terms
- Factor expressions
- Cancel common factors
- Convert to a common format (decimals to fractions, or vice versa)
The goal is to get both quantities into a form where the comparison is obvious. If you can simplify both sides to the same expression, the answer is (C). If simplification makes one clearly larger, you may not need to test values at all.
Strategy 3: Know When to Pick (D)
(D) is the answer when the relationship depends on the variable's value. But how do you know when that's the case?
The rule: if you can find two valid values for the variable that produce different relationships between the quantities, the answer is (D).
Two values, different relationships. That's the proof.
The most efficient approach is to test two values — one "normal" value and one edge case. If the relationship is the same both times, it's probably consistent (and the answer is A, B, or C). If it changes, the answer is (D).
When should you suspect (D)?
- When a variable appears in one quantity but not the other
- When a variable is raised to a power and the exponent is even (squares can be zero or positive)
- When a variable could be negative (because squaring a negative gives a positive)
- When a variable could be between 0 and 1 (because squaring a fraction makes it smaller)
- When the problem gives a range for a variable (like
x > 0 ) but no specific value
If any of these conditions apply, test edge cases before committing to an answer.
Strategy 4: Geometry QC Questions
Geometry QC questions have a specific trap that catches a lot of test takers: figures aren't necessarily drawn to scale.
On standard multiple-choice geometry questions, the figure is usually drawn to scale. You can sometimes eyeball the answer. But on QC questions, the figure might be misleading. An angle that looks acute might be obtuse. A line that looks like it bisects might not.
The approach: ignore the drawing. Use the rules.
If the question gives you a triangle with two sides labeled, use the triangle inequality theorem. If it gives you a circle with a chord, use the chord properties. Don't rely on what the figure looks like — rely on what the rules tell you.
This is especially important for (D) answers. A geometry QC question where the figure isn't drawn to scale is often a (D) question. The figure shows one configuration, but the given information allows other configurations that produce a different relationship.
Example:
A circle has radius
r .Quantity A: The area of the circle
Quantity B: The circumference of the circle
Test
Test
Test
The relationship changes. The answer is (D).
Worked Examples
Let's walk through a few QC questions to see how the strategies work together.
Example 1: The Simplification Shortcut
x \neq 0 Quantity A:
\frac{3x + 6}{3} Quantity B:
x + 2
Simplify Quantity A:
Both quantities simplify to
No need to test values. No need to pick numbers. The simplification makes the comparison obvious.
Example 2: The Edge Case Trap
x is an integer.Quantity A:
x^2 Quantity B:
x
Test
Test
The relationship changed. The answer is (D).
If you only tested
Example 3: The "Looks Obvious" Trap
n is a positive integer.Quantity A: The number of prime numbers between 1 and
n Quantity B:
n - 2
Test
Test
Test
The relationship changes. The answer is (D).
This question looks like it might have a consistent relationship. It doesn't. Three values, three different relationships. That's (D).
The Most Common Traps
QC questions are designed to catch specific habits. Here are the traps that tend to appear most often.
Trap 1: Assuming Variables Are Positive Integers
When a question says "x is a positive integer," that's a constraint. When it says nothing about x, x could be anything — zero, negative, a fraction.
The fix: before you test values, check what the question tells you about the variable. If it doesn't restrict the variable, test edge cases. Zero, negative, and fractions between 0 and 1 are the ones that tend to change the relationship.
Trap 2: Over-Calculating
You see a QC question with variables and your instinct is to calculate both sides. But calculation is often unnecessary — and it takes time.
The fix: before you calculate, check if simplification makes the comparison obvious. If both quantities simplify to the same thing, you're done. If one simplifies to something clearly larger, you're done. Save calculation for when simplification doesn't resolve the comparison.
Trap 3: Forgetting (D) Exists
A lot of test takers default to (A), (B), or (C). They find a relationship for one value and commit. (D) doesn't occur to them because they're thinking in terms of "which is bigger" — not "can we tell which is bigger."
The fix: after you find a relationship for one value, ask yourself: "Does this hold for every valid value?" If the question involves a variable with no specific value, test an edge case before committing. If the edge case changes the relationship, the answer is (D).
Trap 4: Trusting the Figure
Geometry QC questions may include figures that aren't drawn to scale. An angle that looks like 45 degrees might be 30. A triangle that looks isosceles might not be.
The fix: ignore the visual proportions of the figure. Use only the information explicitly given — labeled angles, side lengths, and geometric rules. If the figure shows a specific configuration but the given information allows multiple configurations, the answer is probably (D).
Timing and Pacing
QC questions should take less time than standard multiple-choice math questions. The reason: you often don't need to calculate. Simplification and testing values are faster than solving.
A good target is 60 to 90 seconds per QC question. If you're spending more than two minutes on a QC question, you're probably over-calculating.
The exception is geometry QC questions, which may take a bit longer if you need to work through multiple rules. But even those should resolve in under two minutes if you know the rules.
If you're stuck on a QC question after 90 seconds, make your best guess and move on. One wrong answer probably won't sink your score. Running out of time on later questions will.
How to Practice QC Effectively
Knowing the strategy is one thing. Building the habit is another. Here's how to make practice count.
Practice Testing Edge Cases on Every Variable Question
When you practice QC questions with variables, make it a habit to test at least two values — one "normal" value and one edge case. Even on questions where the answer is (A), (B), or (C). The habit of testing edge cases is what catches (D) answers on test day.
After each question, ask: "Did you test zero? A negative? A fraction?" If the answer is no, go back and test those values. Over time, the habit becomes automatic.
Review Wrong Answers by Finding the Assumption
Every time you get a QC question wrong, go back and figure out what assumption you made. Did you assume the variable was positive? Did you trust the figure? Did you forget that (D) was an option?
Write down the assumption and the edge case that would have caught it. Over time, you may start recognizing your own patterns — the assumptions you tend to make — and catch them before they cost you points.
Practice With Official ETS Materials
The GRE® is written by ETS, and the style of their QC questions is distinctive. Third-party prep companies write reasonable approximations, but the logic of real ETS questions is hard to replicate. The way ETS builds in traps — especially (D) traps — follows patterns that you can only learn by practicing with real questions.
Use the official GRE® PowerPrep tests and the Official Guide to the GRE® as your primary practice sources. Save third-party material for additional volume.
Time Yourself
Because QC questions should be faster than standard math problems, timing matters. When you practice, time each question. If you're consistently over 90 seconds, look for where you're spending time. You're probably calculating when you could be reasoning.
Frequently Asked Questions
What are the answer choices for GRE® Quantitative Comparison questions?
Every QC question has the same four answer choices:
(A) Quantity A is greater. (B) Quantity B is greater. (C) The two quantities are equal. (D) The relationship cannot be determined from the information given.
The answer choices are always in this order. Memorizing them saves you time on test day — you don't have to read all four before selecting your answer.
How many Quantitative Comparison questions are on the GRE®?
QC questions make up roughly 40 percent of the GRE® Quant section. The Quant section has two parts — the first with 12 questions and the second with 15. Across both sections, you can expect approximately 11 to 14 QC questions. The exact number varies, but QC is a significant portion of your Quant score.
Should you always test numbers on QC questions with variables?
Not always. If you can simplify both quantities and the comparison becomes obvious, you don't need to test values. But if simplification doesn't resolve the comparison — or if the question involves a variable with no specific value — testing values is the most reliable approach. When you test, make sure to include edge cases: zero, negative numbers, and fractions between 0 and 1.
When is the answer (D)?
The answer is (D) when the relationship between the quantities depends on the value of the variable. If you can find two valid values that produce different relationships, the answer is (D). The most common (D) scenarios involve variables that could be zero, negative, or fractions — because those values tend to change the relationship between the quantities.
Are geometric figures drawn to scale on QC questions?
Figures on QC questions aren't necessarily drawn to scale. This is different from standard multiple-choice questions, where figures are usually drawn to scale. On QC questions, the figure may be misleading. Use only the information explicitly given — labeled angles, side lengths, and geometric rules. Don't rely on visual proportions.
Are Quantitative Comparison questions harder than regular math questions?
They're different, not necessarily harder. Some test takers find QC questions easier because they often require less calculation. Others find them harder because the format is unfamiliar and the traps are different. If you're strong at math but struggling with QC, the issue is usually approach, not knowledge. Learning the QC-specific strategies — edge cases, simplification, and (D) awareness — tends to close the gap quickly.
Can you use a calculator on QC questions?
Yes — the GRE® provides an on-screen calculator for the Quant section. But QC questions are designed to be solvable without heavy calculation. If you find yourself using the calculator a lot on QC questions, you may be over-calculating. Look for simplification or reasoning shortcuts first. Use the calculator as a backup, not a default.
How long should you spend on a QC question?
A good target is 60 to 90 seconds. QC questions should generally be faster than standard multiple-choice math questions because they often don't require full calculation. If you're spending more than two minutes on a QC question, you may be over-calculating. Make your best guess and move on if you're stuck after 90 seconds.
Want to learn even more?
If you're building a GRE® study plan and want to see how QC fits into the bigger picture, our complete GRE® study guide covers every section and study technique. For a full breakdown of what the Quant section tests, our guide on what's on the GRE® walks through every question type in detail.
If you're hitting a wall on QC specifically, our guide on breaking through a GRE® score plateau covers how to diagnose and fix score stalls across both sections. And if you're just getting started, our guide on how to start your GRE® studies helps you build a foundation from day one.
You can also visit us at thegrestrategy.com for more resources and information about working with us directly.