GRE Quantitative Comparison
Quantitative Comparison is the GRE's signature question type: you are shown Quantity A and Quantity B and asked which is bigger. You almost never need exact values, just the comparison, which is what makes QC fast once you have a method.
The four choices never change
- (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.
They are identical on every QC question. Learn them once so you spend your time on the math, not re-reading the options.
Simplify both sides in parallel
Treat the comparison like a balanced scale. You can add or subtract the same quantity from both sides, and multiply or divide both by the same positive number, without changing which side is larger. The one rule you cannot break: never multiply or divide by a variable unless you know its sign, because multiplying an inequality by a negative flips it. Stripping away what both sides share often leaves an obvious winner.
Plug in smart numbers
When variables are involved, test values that behave differently: 0, 1, a fraction between 0 and 1, a negative, and a large number. Fractions and negatives are where intuition breaks (squaring a fraction makes it smaller, a negative makes it positive). If one value makes Quantity A larger and another makes Quantity B larger, you are done: the answer is D.
The D rule, and the traps
“Cannot be determined” is about the relationship varying, not about you not knowing the exact numbers. The crucial corollary: if both quantities are pure numbers with no variables, D is impossible, a numeric comparison always has a definite answer. Two more traps: do not assume a variable is a positive integer unless told, and never trust a geometry figure's proportions, QC figures are not drawn to scale.
Frequently asked questions
What are the four answer choices in GRE Quantitative Comparison?
They never change: (A) Quantity A is greater, (B) Quantity B is greater, (C) the two quantities are equal, and (D) the relationship cannot be determined from the information given. Memorize them so you do not reread them each time.
When is the answer D, cannot be determined?
Only when the relationship can genuinely change. If plugging in different legal values flips which side is bigger, it is D. But if both quantities are pure numbers with no variables, the answer can never be D, because a definite comparison always exists.
Can I simplify both quantities like an equation?
Yes, with one caution. You can add or subtract the same thing from both sides, and multiply or divide both by the same POSITIVE number, without changing the comparison. Never multiply or divide by a variable that might be negative or zero.
What numbers should I plug in?
Test the ones that expose different behavior: 0, 1, a fraction between 0 and 1, a negative number, and a large number. If any choice gives a different relationship than another, stop and pick D.
Practice QC with real GRE questions
Grezi drills Quantitative Comparison with adaptive practice and an AI tutor that flags when you forgot to test a fraction or a negative, the mistakes that make QC feel random.
More GRE Quant: all topics, formula sheet.