StrategyQuantitative · Verbal · Data Insights

How to review a wrong GMAT question

Review is not complete when the explanation makes sense.

It is complete when you can identify the first decision that diverged, state a correction rule you can execute, and apply that rule to a nearby question.

1. Re-solve before reading the explanation

Hide the answer and attempt the question again without time pressure.

This separates two situations:

You can solve it untimed: timing, recognition, or route selection may be the issue.
You still cannot solve it: concept or reasoning structure may be missing.

Do not let the correct answer become a hint.

2. Find the first divergence

Compare your work with a valid route. Stop at the first place your reasoning changed.

The first divergence may be:

misidentified target
wrong concept selected
incorrect translation
missing constraint
lost sign or case
unsupported inference
correct route executed badly

The final wrong calculation is often downstream noise.

3. Classify the failure

Use three layers:

Concept

Was the required rule or relationship unavailable or wrong?

Reasoning trap

Was the concept available but represented or applied incorrectly?

Execution

Was the plan correct but the arithmetic, reading, or timing execution faulty?

More than one can apply. Record the primary cause and one contributing cause at most.

4. Write a portable correction rule

Bad rule:

Be careful with percentages.

Useful rule:

Before dividing, label the numerator and the reference base in words.

Bad rule:

Read the question properly.

Useful rule:

Write the requested object and units before calculating; restate what the result means before selecting.

A good rule tells your future self what to do at the moment the mistake would occur.

5. Prove the correction on a transfer question

Re-solving the same item can measure memory. Use a nearby question with different surface details but the same concept or trap.

If the correction works, record the transfer result. If it fails, refine the diagnosis.

Worked review

Question: A fee rises from $80 to $92. What is the percentage increase?

Selected answer: 12%.

First divergence: treated the dollar increase as a percentage.

Classification: Requirement Misread, not a missing percentage formula.

Correction rule:

Match the units of the result with the units requested by the stem.

Transfer:

A quantity rises from 50 to 65. The increase is 15 units and 30%, not 15%.

Problem Solving Very Hard · percent / fractions, decimals

A wine merchant bought 80 cases of wine at $37 1/2 per case and sold them all at $75 per case, paying a 4 percent excise tax on the total purchase price and a 6 percent sales commission on the total selling price. Which of the following is closest to the merchant's percent gain on this investment?

Answer: B

Total purchase price: 80 x $37.50 = $3,000. Purchase fee: 4% of $3,000 = $120, so total investment cost = $3,120. Total sale price: 80 x $75 = $6,000. Sale fee: 6% of $6,000 = $360, so net proceeds = $5,640. Gain = $5,640 - $3,120 = $2,520. Percent gain = $2,520 / $3,120 x 100 = about 80.8%, closest to 81%. The 88% option uses the sale fee but omits the purchase fee; 92% uses the purchase fee but omits the sale fee; 100% omits both fees; 45% divides the gain by net proceeds.

Original GMAT-style question written for Premiergrad and checked by an independent blind solve. Not an official GMAT question.

What Lumen looks for

Lumen reads the answer you chose, not just whether it was wrong. On a question like this it separates three things that all look identical in a score: a concept you have not met, a reasoning step that went sideways, and a correct method pointed at the wrong target. Those need three different next weeks, and only the third one is fixed by re-reading the topic.

A single answer is weak evidence and Lumen says so. It becomes a diagnosis when the same shape shows up across several questions — which is the part a page like this cannot do for you.

The five-line review template

Target: What exactly was asked?
First divergence: What was the first wrong decision?
Classification: Concept, trap, or execution?
Correction rule: What will I do next time?
Transfer result: Did the rule work on a nearby problem?

Use the template freely. If you want the attempt, answer choice, likely trap, and follow-up practice connected automatically, try the Premiergrad diagnostic quiz.

Review one question with Lumen →

Index Trap Library index
A trap is not a topic you have not studied. It is a decision that goes wrong in a predictable place.

The vocabulary this review procedure classifies into.
Strategy Why Careless Errors Aren’t Really Careless
“Careless” describes how a mistake feels after you see it. It does not explain what produced it.

What to do when the review keeps saying "I knew that".
Trap Requirement Misread
A Requirement Misread occurs when your work answers a nearby question rather than the exact one asked. The arithmetic…

The most common first divergence.

You have the method — now get the evidence

A framework is worth more with your own attempts in front of it. A short diagnostic produces the evidence this page tells you how to read.

Run a short diagnostic Everything on this page stays free and open — no account needed to read it or to attempt the questions above.

Last reviewed 2026-09-17