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GMAT Quantitative Errors: Understanding Incorrect Answers

When most people miss a GMAT quant question, the ensuing chain of events tends to be some version of the following: refer to the answer explanation, make sure they understand the explanation, re-do the question, and move on to the next question. Though such an approach certainly benefits test-takers whose only issue is conceptual, it grossly oversimplifies the numerous factors involved in the problem-solving process. To understand why you missed a GMAT question and to maximize what you learn from that question, your review process should involve more than simply understanding how the test-makers at GMAC (or at a certain company) recommend solving a problem.

The fact is that your goal when reviewing a question is to understand why you missed it, and to develop generalizable takeaways from this process. But understanding an explanation does not mean you understand why you missed the question! This is the more pertinent issue when it comes to “solving, reviewing, moving on.” Yes, if there’s a conceptual issue, the explanation in the book might give you some insight into a topic you previously didn’t understand, but what about the situations where your issue had less to do with the topic and much more to do with how you actually thought of the question — a fact that merits substantial consideration since the GMAT is, after all, a reasoning test. If you’re not equipped with the right way of reviewing questions, then you’ll be making sub-optimal use of your study time, focusing only on rules at the expense of developing generalizable takeaways from the questions you’ve missed — takeaways that can be of vital assistance on test day. So, when reviewing a question, what else is there to focus on? Generally, I lump reasons for missing Quant questions into a few categories.

#1) conceptual: did you understand the actual content tested? If you didn’t, then this is an ideal time to review the content from a strategy guide/video service, and to do some additional questions corresponding to that topic. Knowledge of the core GMAT quantitative content is a pre-condition for higher GMAT scores, and when you identify a deficiency, you should work to plug that hole as efficiently as possible.

#2) strategic: This is where things get interesting. Strategy can mean a lot of things, but basic strategic errors include the following:
– did you look at the choices before you started solving?
– did you consider strategies such as variable substitution or backsolving?
– did you make sure to have a concrete plan of attack before you started answering the question?
– did you note important words such as “approximately,” “estimated,” “closest to,” etc.
– if you tested cases in data sufficiency, did you test the right numbers?

Note that none of the above concern your understanding of a certain topic. Rather, they relate to your ability to consider a question from every angle, to identify test-taking approaches, and reason through a situation as efficiently as possible. It’s these kinds of skills that differentiate a good score from a great one.

#3) prompt-based: Did you make an assumption? Did you overlook information? Did you answer the wrong question? Oftentimes, students categorize these errors as “silly mistakes,” but these are errors fundamental to the problem-solving process. In fact, many trap answers are designed with these errors in mind. These mistakes, though usually attributable to rushing, can oftentimes be the source of immense frustration if you don’t slow down and work on addressing them.

#4) Algebra/Arithmetic mistake: This final category is what some traditionally call “careless errors”. It can be as simple as adding two to both sides instead of subtracting two, or forgetting to flip the arrow when multiplying across an inequality by a negative. As is the case for category #3, errors of this type can be insidious, often foiling the attempts of students who have achieved full content mastery but have neglected to address the finer points of their problem-solving approach.

As you go through your GMAT preparation, my suggestion is that you parse through questions you’ve missed with a fine-toothed comb. Remember that a missed question is a teachable moment. Understanding the explanation in a book is certainly helpful, but identifying why you missed a question and your specific tendencies will pay far more dividends on test day.


Erfun Geula
Erfun Geula

Erfun Geula is a professional GMAT tutor, based in New York City. He has scored in the 99th-percentile of the GMAT three different times, he has written and edited hundreds of practice GMAT questions, and he has over 7,000 hours of tutoring experience.

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