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Which GMAT Problems Should I Guess On? – Part 3: Making Great Guesses on Quant Problems

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Manhattan Prep GMAT Blog - Which GMAT Problems Should I Guess on? - Part 3: Making Great Guesses on Quant Problems by Chelsey CooleyDid you know that you can attend the first session of any of our online or in-person GMAT courses absolutely free? We’re not kidding! Check out our upcoming courses here.

You’ve read a Quant problem, and you’ve realized that you don’t have a plan. How do you make the smartest, fastest guess possible, and increase your odds of salvaging the problem?

Let’s start with Quant Problem Solving problems. Let’s also assume that you’re actually guessing, not using an alternative strategy, such as Backsolving or Choosing Smart Numbers! The following three methods are good ways to make a decent guess even if you don’t have a strategy at all.

  1. Benchmarking

Compare the answer choices to another value. This can be a value in the problem: for instance, imagine a problem that gives you Frank’s weight, and asks you to solve for Alice’s weight. Can you determine, just with logic, whether Alice weighs less or more than Frank? You can also use a common ‘benchmark’ value, such as 1/2, 50%, 1, or 0. Perhaps 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 in under 2 minutes, can you use logic to work out whether the drink is more or less than 50% seltzer? If the answer has to be greater than 50%, eliminate any answer choice that’s below 50%, and vice versa.

  1. Look for ‘evil twins’

In PS problems, the right answer often has an ‘evil twin’ among the answer choices. If the correct answer is 15/23, for instance, then 23/15 will probably be one of the options. If the correct answer is the value of a, 32, and a+b equals 100, then the value of b — 100-32, or 68 — will be an answer choice. The test writers do that because it’s common to accidentally solve for the wrong variable, or flip a fraction or ratio, or make other, similar mistakes. Eliminate answer choices that don’t have ‘twins’ before you make a guess.

  1. Eliminate easy answers

The GMAT is a hard test, and finding the right answer is rarely as simple as just copying numbers from the problem, or adding or multiplying them. If an answer reproduces a value or values from the problem, or if it could be calculated by doing very simple math with those values, it probably isn’t right. Eliminate any ‘too easy’ answers before you guess. Also, the GMAT wants to make you do as much work to simplify the answer as possible. If you’re guessing between ‘25‘ and ‘85‘, pick 25 — 85 could be simplified further, so it’s less likely to be right.

How about Data Sufficiency? Guessing on a Data Sufficiency problem is a bit different. You don’t have to come up with a numerical answer, so you can’t just estimate the answer. But, you can still guess on a problem you don’t know how to solve, by looking for the following clues.

  1. Don’t guess (C)

Why not? After all, (C) is just as likely to be correct as any other answer choice — it’s the right answer on 20% of all Data Sufficiency problems. But, many DS problems are designed so that (C) looks like the right answer to someone who doesn’t understand the problem deeply. If (C) seems right at a glance, but you know that you didn’t really ‘get’ the problem, consider guessing something else.

  1. If the two statements are obviously sufficient together, guess (A), (B), or (D).

If it’s obvious that the two statements are sufficient together, (C) could be the right answer. But, more likely, if you had more time to understand the problem, you’d find a subtle reason that either or both of the statements were actually sufficient alone.

  1. If the two statements are identical, guess (D) or (E).

Sometimes, the statements are mathematically identical, just phrased differently. Here’s an example:

(1) x is y percent of z

(2) 10x is 10 percent of yz

Both of these statements simplify to the same equation: 100x = yz. Because they tell you the same thing, there’s no way that one of the statements is sufficient and the other isn’t. And (C) can’t be right, because you don’t gain any extra insight from combining the statements together. So, guess (D) or (E)!

  1. If the two statements are very similar, guess (A) or (B).

If the two statements look almost alike, the problem is probably testing your ability to find a subtle difference between them. That means the answer is more likely to be (A) or (B).

  1. Know the common Data Sufficiency error types.

The more Data Sufficiency problems you do, the more you’ll recognize problems that are set up in particular ways. Many of those common DS problem ‘flavors’ are described in Part 1 and Part 2 of my blog post series, “Here’s Why You Might Be Missing GMAT Data Sufficiency Problems.”

One great example is the DS problem that includes a ‘nice but not necessary’ statement: one statement is very complex and math-heavy, while the other statement is a single, simple fact. It’s easy to answer the question using both statements, but in fact, the question can often be answered with only the more difficult statement. If you see a problem that fits this mold, a good guess is that the harder statement is sufficient, and the other isn’t.

Getting better at guessing is worth your time! Solving ultra-tough Quant problems isn’t what the GMAT is all about. Attempting 800-level problems is a great way to waste your own time and end up rushing through the easy problems that actually matter. However, if you can answer a tough problem in one or two minutes by guessing, you can enjoy the extra points guilt-free! A few great guesses throughout the Quant section can free up your time for the problems that actually matter, and give you a nice bump to your Quant score. ?

Want full access to Chelsey’s sage GMAT wisdom? Try the first class of one of her upcoming GMAT courses absolutely free, no strings attached. 

Chelsey CooleyChelsey Cooley Manhattan Prep GMAT 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 GMAT prep offerings here.