Prepping for the GRE Test of Your Quant Logic

The GRE math section is, ultimately, testing how you think. This tag applies even more aptly to a specific type of question that appears on the math section called quantitative comparison that gives you two quantities– anything from a simple number to an algebraic representation of a quantity in a given diagram. They always come with the same 4 answer choices, so you can always know what to expect. They are:

A. The quantity in Column A is greater

B. The quantity in Column B is greater

C. The two quantities are equal

D. The relationship cannot be determined from the information given

In GRE parlance, this question type is usually considered distinct from traditional, more straightforward “problem solving” questions.  There is a major difference between the two sections, and that key distinction lies in the word ‘solving’. With quantitative comparison, you want to avoid solving the problem. Instead, you want to be able to think about the problem so that you can answer the question quickly: which side, if any, is bigger?

Thinking logically, however, isn’t always easy. Though it may sound counterintuitive, the more you study a specific concept, the more likely you are to waste time on a quantitative comparison question. The likely reason is that your brain is in solve mode (after all, you’ve been doing a lot of practice), not in look-at-the-big-picture mode. When you take the latter approach, you can approach a problem in a logical fashion, instead of regurgitating a sequence of steps.

If you’ve done enough GRE series questions to the point that you can quickly and confidently add up a series of consecutive problems, you will definitely be able to answer the following question. But, will you be able to spot the quickest way of solving the problem?

Column A Column B
The sum of the multiples of 7 up until 1000 The sum of the multiples of 14 up until 1000

A. The quantity in Column A is greater

B. The quantity in Column B is greater

C. The two quantities are equal

D. The relationship cannot be determined from the information given

Again, by following the formula for adding a series of numbers that differ by a consistent amount, you can solve this problem (though it will take a couple of minutes to do so). Instead, write out the first few multiples for column A and B, and see if you notice any pattern (you may actually notice the pattern without even writing anything down).

Column A Column B
7+14+21+28+35+42 14+28+42

A. The quantity in Column A is greater

B. The quantity in Column B is greater

C. The two quantities are equal

D. The relationship cannot be determined from the information given

What do you notice? Well, every number in Column A is in Column B. However, column A also has more numbers (7, 21, 35, etc.) that are not in column B. Therefore, Column A must be greater than Column B (remember both end at a 1000…994 to be exact).

And that’s it. With just one logical breakthrough, you can save yourself over a minute.

Takeaway:

Know how to solve a problem. But, also know how to look at the big picture, especially on quantitative comparison questions. Often, you’ll find a much faster way of doing a problem without losing accuracy.

This post was written by Chris Lele, GRE and GMAT Expert at Magoosh Test Prep. Magoosh offers hundreds of practice questions and video lessons, as well as free resources and tips on how to master the GRE and GMAT. Read our GRE Study Guides and Plans to learn how to plan a study strategy for the new GRE.

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  • edbtz

    I took both tests recently so here is my take on the GRE vs GMAT. Overall, they are about the same. Interestingly the ETS GRE-GMAT score conversion predicted my score perfectly. It’s on the ETS site.

    Per the math….

    On the old GRE a lot of people got perfect 800s on the math, but those days are gone. The new one has a much higher “top end” for the math, and so it is much harder to get into the very high (160+) range for math.

    I think the GMAT is easier to study for in terms of recognizing frequent question formats. The GRE seemed to have a pretty wide array of problems. This was particularly true in the quant sections because there is a basic calculator.That said, the calculator doesn’t really help much because it only does basic functions and is slow to use. It’s much better to do the calculations mentally except for something like multiple interest compounds.

    Guessing strategies are not as applicable for the new GRE because a lot of the problems ask you to enter the exact answer into a box, and some are “check all correct answers” (usually a range problem). My suggestion if you find yourself short on time and needing to guess on a few, then be sure to answer the “entry box” and “check all” problems first because you cannot guess on these.

  • Sarah

    Hello,
    I am also preparing for GRE and will be taking the test next year which leaves me with ample amount of time to prepare well. Being from an arts background Quant is my weakness & I would not hesitate to say that I dread mathematics. Iv taken a few prep tests and done fairly well in verbal but its just the opposite for quant. I found this online help http://www.wiziq.com/course/25… I am just doubtful if I should go for this.. I want a resource that can help me start with my basics. Please suggest if its good enough.
    Thanks
    Sarah