GRE Answer Choice Tricks, Part 2

January 4, 2013
Boris Dvorkin

GRE BlogLast week, I showed you one trick that the test makers use to “hide” right answers. Here’s a second:

By mathematical convention, square roots shouldn’t appear in the denominators of fractions. The GRE adheres to this convention, which means that the answer you come up with will sometimes look radically (*cough*) different from the credited answer. For example, you might solve a problem and get:

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But when you look at the answer choices, that fraction won’t appear anywhere. The correct answer would actually be Slide029.

This is a scary moment for many of you, since apart from the radical, those two numbers don’t look anything alike! As always, don’t panic. When you get an answer that looks nothing like the choices and there are radicals involved, make sure you don’t have any radicals on the bottom of the fraction. If you do, great! That’s your problem, and it’s an easy one to fix. Multiply the top and bottom of the fraction by any radicals on the bottom — in this case, by the square root of 3 — to “clean up” the fraction:

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Remember, when you multiply a radical by itself, the number doesn’t change — all that happens is the radical “pops off.” And now, the 6 on top cancels with the 3 on the bottom to get Slide029, the answer you can calmly and happily click on Test Day.

Boris Dvorkin Boris scored in the 99th percentile on the PSAT, was a National Merit finalist, and went on to earn two degrees from Case Western Reserve University. As a two-time Kaplan Teacher of the Year, Boris has helped many students achieve their goals and is known for his sense of humor in the classroom. When Boris isn’t helping students tackle tests, he loves playing strategy board games.

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