Quantitative Comparison on the GRE: How to get it right
The Quantitative Comparison (QC) problems on the GRE can feel odd at first. Even after some study, many test takers tense up when a QC item appears. That reaction makes sense. You can do a lot of work, pick one of four choices, and still miss the core idea of the question.
Why does this happen? Because QC is about making quick, confident decisions with limited information. It is less about heavy math and more about comparing two things under time pressure.
What is QC?
The GRE is not a pure math test. It checks how well you analyze, decide, and prioritize when you do not have time to try every path. QC questions ask you to compare two quantities. Your task is to decide which quantity is greater, whether they are always equal, or whether you cannot tell.
Picture a manager asking, “From this data, which one is larger? A, B, or are they the same?” That is QC in a nutshell. Some math is involved, sometimes annoying math, but you often do less calculation than on standard problem-solving questions.
How QC works
Every QC problem shows two columns: Quantity A and Quantity B. There may also be a statement above both columns. If it appears, you must use it.
The core question never changes: which quantity is bigger?
Consider this setup:
Oliver is 4 years older than Sam
Quantity A: Oliver’s age now
Quantity B: Sam’s age in 5 years
Try a value. If Oliver is 10, then Sam is 6. In 5 years, Sam will be 11. For this case, Quantity B is bigger.
Now, think broadly. Whatever Oliver’s age is now, Sam is always 4 years younger. In 5 years, Sam will be 1 year older than Oliver is today. That relationship is always true, so Quantity B is always larger.
QC uses the same four answer choices every time:
- A: Quantity A is always greater
- B: Quantity B is always greater
- C: The two quantities are always equal
- D: The relationship cannot be determined from the information given
The first three choices are always claims. If you cannot prove an always relationship, pick D.
Try one more
Given: x² − 9 = 0
Quantity A: 3
Quantity B: x
Solve the given.
x² = 9, so x = 3 or x = −3.
If x = 3, the quantities are equal. If x = −3, Quantity A is greater. Since the outcome changes, there is no always relationship. The answer is D.
A simple step-by-step plan
- Draw an answer grid with A, B, C, D and cross out choices as you go.
- Read the given statement, then rewrite or simplify it if you can.
- Write short versions of both quantities. Your goal is comparison, not full calculation.
- Eliminate answer choices as soon as you have proof, then pick when one remains or guess and move on if stuck.
How to compare quantities fast
Start by spotting links between the two sides:
- Do both quantities share variables or refer to the same people, shapes, or values?
- Can the given statement connect the two sides in a helpful way?
Then simplify. If both sides look messy, try to simplify them in tandem. You can apply the same moves to both sides if they are valid for inequalities:
- Add or subtract the same value on both sides
- Square both sides, or take square roots if both quantities are known to be nonnegative
- Multiply or divide by the same positive number
Example:
Quantity A: x² − 4x + 2
Quantity B: x² − 6x + 9
Both sides include x². Subtract x² from both:
Quantity A: −4x + 2
Quantity B: −6x + 9
Add 4x to both:
Quantity A: 2
Quantity B: −2x + 9
Now compare 2 and −2x + 9.
Pick test values, since x has no restrictions.
- If x = 10, Quantity B is −11, so Quantity A is greater. Cross off B and C.
- If x = −10, Quantity B is 29, so Quantity B is greater. Cross off A.
You cannot lock in A, B, or C, so the answer is D.
Getting stronger at QC
You can improve a lot with the right habits:
- Test simple numbers, including negatives, zero, fractions, and large values
- Look for always statements you can prove or disprove
- Use algebra to link the quantities, but stop as soon as you can compare
Want structured practice or coaching? Check out tutoring and courses here: https://testprepistanbul.com/en/gre-prep-course-gre-tutoring/.
You will need a solid base of math, but QC rewards smart comparisons and clear thinking. Learn the rules, practice the patterns, and keep your work short and purposeful.