GMAT Tip: Using Answer Choices to Solve Problems

GMAT Tip: Using Answer Choices to Solve Problems
Sometimes clues to answering difficult GMAT questions are hidden in plain sight: in the answer choices themselves (Photograph by Robert Payne/Getty Images)
Photograph by Robert Payne/Getty Images

This tip on improving your GMAT score was provided by Brian Galvin at Veritas Prep.

Business is in large part about leveraging assets; accordingly, the GMAT is much the same. After all, efficient market theory tells us that most assets—plots of land, factories, divisions of  companies—are priced as the market sees their value. The winners in business are those that can extract more value from an asset than this. If you had purchased tracts of land in Hoboken, N.J., in the 1970s, on seeing that a boom in Manhattan real estate might send businesses and yuppies across the Hudson for slightly-cheaper rent and even-better skyline views, you’d be a multimillionaire now for having seen extra value in assets.

The GMAT tests that concept frequently. Examinees can maximize the value of the assets given within each question. And one of the most overlooked, most underused assets on nearly any problem-solving question on the quantitative section is the choice of answers.

Answer choices give you plenty of insight into questions. Sometimes you can simply plug them back into the question to test which one works. Other times you can quickly eliminate a choice or two for not fitting the general parameter of the question. Even more underutilized, though, are clues in the answer choices that tell you want kind of math you need to perform. Consider the question:

Three identical circles of circumference 12π are each tangent to one another at exactly one point. What is the area of the shaded region?

A) 9 – 18 π

B) 18 – 12 π

C) 36 – 36 π

D) 36  – 18 π

E) 36  – 6 π

This problem involves some tricky spatial thinking with regard to geometry. But if you don’t see immediately that you can use the radii of each circle to form a triangle, you can get a further clue from the answer choices. Each involves pi, which is expected in a question that involves circles. Each also involves the square root of 3. And where does the square root of 3 usually come from in a GMAT context? Frequently, it’s 30-60-90 triangles, or equilateral triangles.

Based on that clue in the answer choices, you should start looking for where an equilateral or 30-60-90 triangle might help you. As it turns out, the radii of each circle (each with a length of 6) will connect to form an equilateral triangle surrounding the shaded region:

And then you can take the area of that triangle (which is 36 ) and subtract the pie-slice sections to get the area of the shaded region. Because the angle on each pie slice is 60 degrees—which we know because they’re part of an equilateral triangle—each is 1/6 of the area of one circle.

More important than this question, however, is what it can teach you: The answer choices are major assets. That square root of 3 is a massive clue helping you to jump-start your understanding of the problem. And if you know that pi is 3.14 and the square root of 3 is about 1.7, you can eliminate answer choices such as C, which would be negative (36π will be much larger than 36√3).

So learn to leverage all the assets in problems, including the answer choices. Answer choices can help you through:

• Process of elimination

• Backsolving (plugging in answer choices to see which works)

• Clues to help you get the math started

Winners in business are those who can squeeze the most value out of their assets; winners on the GMAT do so by the same principle. Leverage your assets toward GMAT success.

Brian Galvin has studied the GMAT full time since 2006 as the director of academic programs for Veritas Prep. He received a Masters in Education from the University of Michigan and is the proud owner of a 99th percentile GMAT score.

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