Quantitative Comparison Strategy
Quantitative Comparison (QC) is the GRE’s signature question type, and it is unlike anything on other tests. You are shown two quantities — Quantity A and Quantity B — and asked only which is larger, not to compute either one exactly. The four answer choices are always the same, in the same order, on every QC question, so you can memorise them once and never re-read them. The winning mindset is comparison, not calculation: you rarely need a final value, just the relationship. That opens up fast tactics — simplifying both columns in parallel, testing a few well-chosen numbers, and recognising when a relationship can flip (which forces the "cannot be determined" answer). This chapter drills the four-choice framework and the three techniques that solve the overwhelming majority of QC questions on test day.
Topics
⚡ GRE shortcuts & speed methods
The fastest ways to crack this chapter under time pressure — the techniques that separate a 95+ percentiler from the rest.
- Memorise the four choices once: A greater / B greater / equal / cannot be determined. Never re-read them.
- If both quantities are plain numbers, cross off D immediately — fixed numbers always have a definite order.
- Treat the comparison like a scale: add or subtract the same thing from both sides, or multiply/divide both by the same POSITIVE number, freely.
- Cancel shared terms before computing — often the variable drops out and the answer falls out in one line.
- When variables appear, test 0, 1, a negative and a fraction between 0 and 1 — the values that expose flips.
- Two allowed test values giving opposite relationships PROVES the answer is D. Stop as soon as you find them.
- GRE geometry figures are "not drawn to scale" — reason from the given measurements, never from how the picture looks.
⚠️ Common mistakes & traps
GRE is designed so that careless errors here cost you marks. Internalise each trap before the exam.
- Picking D when both quantities are specific numbers (D is then impossible).
- Multiplying or dividing both quantities by a variable whose sign is unknown — a negative flips the inequality.
- Testing only easy positive integers and missing the flip that 0, a negative or a fraction would reveal.
- Squaring both sides when a quantity could be negative, breaking the comparison.
- Trusting a not-to-scale figure’s appearance instead of the labelled measurements.
- Fully computing each quantity when cancelling a shared term would answer the question far faster.
📈 GRE exam insight & question patterns
A QC shows two purely numeric quantities. Can the answer be D?
No. Two specific numbers always have a fixed relationship, so D is off the table — choose among A, B and C.
When is choice D the correct answer?
Exactly when you can find two allowed scenarios giving opposite relationships. One counterexample to "always A" plus one to "always B" proves D.
Quantity A: x²; Quantity B: x, with no restriction on x. What is the answer and why?
D. x = 2 makes A bigger; x = 1/2 makes B bigger. The unrestricted variable lets the relationship flip.
A GRE geometry QC gives a figure "not drawn to scale". How should you treat the picture?
As a rough sketch only. Use the stated measurements and properties; if the unstated parts can vary, the answer is often D.
Is it safe to multiply both quantities by x to clear a fraction in a QC?
Only if you know x is positive. If x could be negative the inequality flips, and if x could be 0 the move is invalid — so usually avoid it.
🎴 Flashcards — instant recall
Tap a card to reveal the answer. Drill these until they are automatic.
📌 Quick revision
- The four QC choices are fixed and ordered — memorise them so you can compare, not re-read.
- If both quantities are specific numbers, the answer is never D; choose A, B or C.
- Simplify both quantities in parallel: add/subtract equally, or multiply/divide by the same positive number, to strip shared clutter.
- Never multiply both sides by an unknown that could be negative — the inequality would flip.
- For variable QCs, plug in 0, 1, a negative and a fraction; these expose relationship flips.
- The answer is D exactly when two allowed values yield opposite relationships — find one counterexample each way.
- Treat GRE figures as not to scale; reason from the given measurements, and lean toward D when unstated parts can vary.
Chapter test
🏆 Vidaara GRE success checklist
You have truly mastered Quantitative Comparison Strategy when you can tick every box below.
- Recall every formula in this chapter without looking them up
- Solve each topic’s practice set with at least 80% accuracy
- Use the chapter shortcuts to cut your solving time in half
- Spot and avoid every common trap listed above
- Score 80%+ on the timed chapter test
📋 Chapter mastery scorecard
Track where you stand. Aim for the target before moving to the next chapter.
| Skill checkpoint | Target |
|---|---|
| Concept theory & formulas understood | 100% |
| Topic practice sets attempted (4 topics) | 4/4 |
| Best topic-test score | — → 80%+ |
| Chapter test score | — → 80%+ |
| Flashcards drilled to instant recall | 8 cards |
Formula Reference Sheet
The four fixed answer choices (memorise)
| Choice A | Quantity A is greater |
|---|---|
| Choice B | Quantity B is greater |
| Choice C | the two quantities are equal |
| Choice D | the relationship cannot be determined from the information given |
Legal moves on a comparison
| Add / subtract the same amount from both | relationship is unchanged |
|---|---|
| Multiply / divide both by the same POSITIVE number | relationship is unchanged |
| Multiply / divide both by a NEGATIVE number | the inequality FLIPS |
| Choice D is impossible when | both quantities are fixed numbers |