Here’s How to Make a Great Guess on a GRE Quant Problem


Manhattan Prep GRE Blog - Here's How to Make a Great Guess on a GRE Quant Problem by Chelsey Cooley

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Imagine this: you’re at the end of a GRE Quant section, and you have three minutes left. You’ve marked a couple of problems, using the “Good, Bad, and Ugly” technique. Unfortunately, when you look through those problems, there aren’t any that you know you could solve within three minutes. So, what do you do? You’re going to have to guess.

However, because you’ve got a few minutes left, there’s no need to guess at random! Let’s examine two ways to make thoughtful, intelligent guesses on GRE Quant problems.

1. Benchmarking

This technique is great for word problems. Compare the answer choices to another value, and see how they measure up—are they too large, too small, or just right? You could compare the answers to a value in the problem itself: for instance, imagine a GRE Quant problem that gives you Frank’s weight, and asks you to solve for Alice’s weight. Can you determine, just using logic, whether Alice weighs less or more than Frank? You can also measure the answer choices against common ‘benchmark’ values, such as ½, 50%, 1, or 0. Maybe you’re doing a weighted average problem, and you want to know what percent of a drink is composed of seltzer water. Even if you can’t come up with an exact value mathematically, can you use logic to work out whether the drink contains more than 50% seltzer, or less than 50%?

2. Visual Estimation

Have you ever noticed that some GRE Geometry problems include a disclaimer: “figure NOT drawn to scale”? Have you ever noticed that not every geometry problem includes it? That’s because sometimes, the figures actually are drawn to scale. And if they aren’t, you might be able to redraw them more accurately on your own paper! If so, all you need to do is look at the answer choices, and pick one that best matches what you see in the figure. This approach doesn’t work on every Geometry problem, and you shouldn’t use it on Quantitative Comparison problems, but it works often enough that everyone should consider it as a possibility. It may also be useful on some Data Interpretation problems.

Okay, now it’s time to practice. Set a timer for two minutes, and use that time to guess on both of these problems from the 5lb. Book of GRE Practice Problems. Can you eliminate answers that are too large or too small? Can you eliminate answers that don’t ‘look right’?

Problem 1: Working continuously 24 hours a day, a factory bottles Soda Q at a rate of 500 liters per second and Soda V at a rate of 300 liters per second. If twice as many bottles of Soda V as of Soda Q are filled at the factory each day, what is the ratio of the volume of a bottle of Soda Q to a bottle of Soda V?

(A) 3/10

(B) 5/6

(C) 6/5

(D) 8/3

(E) 10/3

Manhattan Prep GRE Blog - Here's How to Make a Great Guess on a GRE Quant Problem by Chelsey Cooley - Geometry Problem Figure

Problem 2: In the figure above, what is the value of x?

(A) 2.5

(B) 5/√2

(C) 5

(D) 5√2

(E) 10/√2

Guessing solutions: In Problem 1, the factory bottles about half as much Soda V as it does Soda Q, in terms of liters. But it also bottles twice as many bottles of Soda V. Each bottle of Soda V must be much smaller. So, the ratio must be much greater than 1. The only reasonable answers are (D) and (E). (E) is closer to 4 times as much soda, so (E) is a better guess.

In Problem 2, the figure is drawn to scale already. x appears to be almost exactly half the length of the only other labeled line in the problem, which has length 10. So, x‘s length is either 5, or very close to 5. The only answers that are close are (C) and (E)—I’d recommend guessing (C). 📝

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Chelsey CooleyChelsey Cooley Manhattan Prep GRE Instructor is a Manhattan Prep instructor based in Seattle, Washington. Chelsey always followed her heart when it came to her education. Luckily, her heart led her straight to the perfect background for GMAT and GRE teaching: she has undergraduate degrees in mathematics and history, a master’s degree in linguistics, a 790 on the GMAT, and a perfect 170/170 on the GRE. Check out Chelsey’s upcoming GRE prep offerings here.

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