GMAT by the Numbers: Algebra

Now that you’ve learned how to approach algebra questions on the GMAT, let’s add one more dimension to your understanding of how they work.

Take a moment to try this question. Following is performance data from thousands of people who have studied with Kaplan over the decades. Through analyzing this data, we will show you how to approach questions like this one most effectively and how to avoid similarly tempting wrong answer choice types on Test Day.

  1. What is the value of g?
    1. f + g = 9
    2. 3f − 27 = −3g
    1. Statement (1) ALONE is sufficient, but statement (2) is not sufficient.
    2. Statement (2) ALONE is sufficient, but statement (1) is not sufficient.
    3. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
    4. EACH statement ALONE is sufficient.
    5. Statements (1) and (2) TOGETHER are NOT sufficient.

Explanation

This question asks you to find the value of g. Neither statement by itself can give you that value, since each contains the variable f as well.

It’s tempting to think as one-fourth of test takers did: the statements together will be sufficient because you can rewrite Statement (1) as f = 9 − g, substitute into Statement (2), and then solve for g. But that’s only tempting to a test taker who doesn’t first simplify Statement (2):

This is the same equation as Statement (1), so it doesn’t add any new information. Knowing that f + g = 9 isn’t enough to know the value of g, so the statements are insufficient even when combined. Choice (E) is correct.

GMAT questions rarely give you algebraic statements in their most useful form. It’s a safe bet that you’ll need to simplify or reexpress almost all the algebra you see on Test Day. Doing so will help you steer clear of common wrong answers and keep you on the road to a higher score.

More GMAT by the Numbers . . .

To see more questions with answer choice statistics, be sure to review the full-length CATs in your online resources.