GMAT Gurus Speak Out: The Secret of Data Sufficiency Values

Vivian Kerr is a regular contributor to several GMAT and SAT websites, allowing her to flex her intellectual muscle while she is in between film and stage projects as an actress.

Data Sufficiency: Value Questions Can Be Sufficient Without Values! That may sound confusing, but it’s true! We’re used to separating “yes or no” data sufficiency from “value” data sufficiency by what is required by each for sufficiency. For a “yes or no” data sufficiency, we need either an exclusive “yes” or an exclusive “no.” For a “value” data sufficiency, we need a single numerical answer. To get that numerical answer, however, you may not always need the values you think you need!

For example, a question asking for the value of the area of the triangle, we’d assume we would have to know the length of the base and the height. But do we really need those values? No! We could also be given information that would lead us indirectly to the product of the base and height. Tricky data sufficiency value questions will often be sufficient in a roundabout way, giving you what you need for sufficiency in a way you didn’t expect.

Let’s look at how the GMAT does this in a ratio question:

(1) A line is graphed on a coordinate plane. How many times less is the distance between the y-intercept and the x-axis than the distance between the x-intercept and the y-axis?

  1. The slope of the line is -9/13.
  2. The y-intercept is located at (0, 26).

Here we might start by assuming we need both distances: from the y-intercept to the x-axis, and from the x-intercept to the y-axis. But do we really? The phrase “times less” tells us it’s really the ratio we’re looking for – how much greater is the second value than the first value? Let’s draw these values to get a sense of what their relationship might be to one another.

The second value (the green line) is the “run” and the first value (the purple line) is the “rise” for an unspecified line.  We know that rise/run = slope, so this value question is essentially asking for the slope, albeit in a roundabout way. If we can find the slope, a statement will be sufficient!

With that in mind, the statements are easy. The first statement is obviously sufficient on its own, and the second statement is not. The purple line is exactly 9/13th times “less” than the green line. The second statement contains helpful information, but just knowing the y-intercept does not give us the ratio between the purple/green lines because we still don’t know the x-intercept.

The correct answer is (A).

Remember on Test Day to look out for value questions that don’t require values! A sum, a product, or a ratio will often suffice, and the component parts are not always as important as we sometimes think! If you can see “through” the question before reading the answer choices, you’ll be on your way to thinking like the test-maker!

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