About 9 of your 27 Quant questions are Quantitative Comparison (QC). That is one-third of your Quant score coming from a single question format. If you have not built a specific system for this format, you are leaving points on the table.
QC is the most learnable question type on the GRE. The answer choices never change. The logic is consistent. Once you internalize the framework, you can solve most QC questions faster and more reliably than standard multiple-choice problems.
The Format
Every QC question shows you two quantities: Quantity A on the left, Quantity B on the right. Sometimes there is a centered condition above both (a value of x, a constraint, a geometric setup). Your job is to compare them.
The four answer choices are always, without exception:
- 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 are not solving for a number. You are determining the relationship between two expressions. This is a fundamentally different task than most math problems, and it requires a different approach.
When D Is Not an Option
This is the most overlooked rule in QC: if both quantities are fixed numerical values, D is never the answer.
If Quantity A is 3^4 and Quantity B is 80, you do not need to know whether x is positive or negative. There is no x. Just compute: 3^4 = 81. Quantity A is 81, Quantity B is 80. Quantity A is greater. The answer is A. There is no ambiguity, so D is impossible.
D only applies when the relationship changes depending on the value of a variable. The moment you see fixed numbers with no unknowns, eliminate D immediately.
The Plug-In Strategy
When variables are involved, plugging in numbers is often faster and safer than algebraic manipulation. The goal is not to find one answer. The goal is to test whether the relationship is consistent or whether it changes across different inputs.
Test in this order:
- A positive integer (try 2 or 3)
- Zero
- A negative integer (try -1 or -2)
- A fraction between 0 and 1 (try 1/2)
- A large number (try 100)
If Quantity A is greater for some values and Quantity B is greater for others, the answer is D. If the relationship stays the same across all your tests, that is strong evidence (not a proof, but strong evidence) that the answer is A, B, or C.
Example: Quantity A is x^2, Quantity B is x.
- Plug in x = 2: A = 4, B = 2. A is greater.
- Plug in x = 1: A = 1, B = 1. They are equal.
- Plug in x = 1/2: A = 1/4, B = 1/2. B is greater.
Three different results. The answer is D.
Example: Quantity A is x^2 + 1, Quantity B is x^2.
- Plug in any value: A is always 1 more than B.
- The answer is A, regardless of what x is.
The #1 Trap: Assuming Variables Are Positive
Most people, when they see a variable, assume it is a positive integer. That instinct kills accuracy on QC.
Unless the problem explicitly says "x is a positive integer" or "n > 0," you must test negative values and fractions. The GRE writers know you will default to positive integers. They build problems specifically designed to fail if you skip the negatives.
Any time you see:
- A variable with no constraint
- An expression involving squares or absolute values
- A problem that looks too easy with positive numbers
Test a negative and test a fraction before you commit to an answer.
The #2 Trap: Not Testing Zero
Zero breaks a surprising number of expressions. Anything multiplied by zero becomes zero. An expression that is clearly positive for x = 2 might be zero for x = 0. If zero is in the valid range of the variable, test it.
Example: Quantity A is 3x, Quantity B is 2x.
- Plug in x = 5: A = 15, B = 10. A is greater.
- Plug in x = -5: A = -15, B = -10. B is greater.
- Plug in x = 0: A = 0, B = 0. They are equal.
Three different results. D. The trap is that most people plug in a positive integer, get A, and move on.
Simplification: Treat QC Like an Inequality
One of the fastest approaches on QC is to simplify by manipulating both sides, the same way you would manipulate an inequality.
You can:
- Add or subtract the same value from both sides
- Multiply or divide both sides by the same positive number
- Square both sides if both sides are positive
You cannot:
- Multiply or divide by a variable if you do not know its sign
- Square both sides if either side could be negative
Example: Quantity A is 2x + 7, Quantity B is x + 10.
Subtract x from both sides: Quantity A becomes x + 7, Quantity B stays x + 10. Subtract 7 from both sides: Quantity A becomes x, Quantity B becomes 3.
Now the question is simply: is x greater than 3, less than 3, or equal to 3?
If no constraint is given on x, the answer is D. If the problem states x > 5, the answer is A. If the problem states x = 3, the answer is C.
This approach turns an algebraic comparison into a much simpler question.
Geometry QC: No Scale to Trust
On QC geometry problems, the figures are not drawn to scale. Do not look at a figure and assume that one angle looks bigger or that two lines look equal. The only information you can trust is what is stated in the problem.
This is different from Data Interpretation, where the charts are drawn to scale and you can read values visually. In QC geometry, the visual is a placeholder, not a measurement. Solve from the labeled values and given constraints only.
Pacing: 75-90 Seconds Per Question
At 75-90 seconds per QC question, a full section of 9 QC questions should take roughly 11-14 minutes. That leaves you the bulk of your time for the more computation-heavy Problem Solving questions.
QC should be faster on average than PS because you are not solving for a specific numerical answer. You are only determining a relationship. Once you find that the relationship is definitive or changes, stop. You do not need to fully evaluate both quantities in every case.
If you are regularly spending more than 90 seconds on QC, the problem is usually one of two things:
- You are doing full algebra when a plug-in would be faster.
- You are not eliminating impossible answer choices early.
Train yourself to ask: "Can I eliminate D right now?" and "Can I simplify both sides before solving?" Those two questions alone will cut your average QC time significantly.
Why QC Is the Most Learnable Question Type
The format is fixed. The four answer choices never change. The logic is always the same: is the relationship consistent, or does it depend on the variable?
Most QC errors come from one of three sources:
- Assuming variables are positive and not testing other cases
- Missing zero as a test value
- Multiplying both sides by a variable without checking its sign
All three are habits, not knowledge gaps. You can fix habits with deliberate practice.
Work through 20-30 QC problems with a specific focus on plug-in testing. After each problem, ask yourself: did I test positive, zero, negative, and a fraction? If you build that checklist into your process, your QC accuracy will go up before your algebra improves at all.
The GRE lessons in Module 7 cover QC strategy in detail, including when to simplify algebraically and when to go straight to plug-in. Once you have the strategy down, reinforce it with the practice builder, where you can filter by QC question type and drill until the approach is automatic.
The QC Decision Tree
When you see a QC problem, run through this sequence:
- Are both quantities fixed numbers with no variables? If yes, just compute. D is impossible.
- Is there a variable? If yes, plug in: positive integer, zero, negative integer, fraction, large number.
- Did the relationship change across inputs? If yes, the answer is D.
- Did the relationship stay the same? Verify by simplifying algebraically if possible, then commit.
- Is this a geometry problem? Trust only labeled values, not the figure.
Nine questions, one-third of your Quant score, consistent logic. There is no Quant question type with a higher return on investment for targeted practice.