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GRE Math Techniques – The Power of Estimation

Many of us, when we first see a math question, hone in on it with laser-like focus. We make sure we read all the relevant parts, and then work out a solution to the problem. Only then do we look at the answers.

There is nothing inherently wrong with approaching a math problem this way; often times, it yields the right answer. But the GRE is a timed test, and solving for the exact answer to every problem is only going to eat up time.

Is there another—almost magical—way of solving a GRE math problem? Well, yes, depending on how you define magic. Once I show you the following technique, and you are able to apply it, you may very well think it magical.

First off, try the following problem.

1. If Machine X can make 40 widgets in 8 minutes, how many widgets can it make in 1 hour?

 

(A) 90

(B) 180

(C) 240

(D) 300

(E) 320

Okay, did you find yourself reading the question, setting up a proportion and then solving for the unknown? If so, no worries. You are simply taking the long approach.

Let’s instead look at the answer choices as soon as we’ve finished reading the question. There is quite a spread between the answer choices, as is often the case with GRE math problems. The range is 90 to 320. If the machine is already pumping up 40 widgets in 8 minutes, it’s definitely going to make more than 90 in 60 minutes. In fact, 60 minutes is almost 8 times as great as 8 minutes. Therefore the machine is going to make almost 8 times more than 40. Well, 8 x 40 = 320 (E), so that’s too big. So, which is number is slightly smaller? (D) 300. And there’s your answer.

This technique is called estimation. Learning to apply it accurately will save you time. It will also help with those more difficult questions, on which you really need your laser-like focus.

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