Official Guide Explanation:
Problem Solving #180




This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Review (12th ed.). Click the links on the question number, difficulty level, and categories to find explanations for other problems.

These are the same explanations that are featured in my "Guides to the Official Guide" PDF booklets. However, because of the limitations of HTML and cross-browser compatibility, some mathematical concepts, such as fractions and roots, do not display as clearly online.

Click here for an example of the PDF booklets. Click here to purchase a PDF copy.


Solution and Metadata

Question: 180
Page: 178
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Descriptive Statistics > Average
Category 2: Algebra > Linear Equations-Two Unk >

Explanation: At first glance, it doesn't look like there will be enough information to solve this problem, but it's worth investigating further. Since the average of x and y is 60, we can say that x + y = 120. Similarly, if the average of y and z is 80, y + z = 160. If we set one of the equations equal to y, we can substitute into the other one, and have a resulting equation that contains only z, x, and a constant.

y = 160 - z

x + (160 - z) = 120

x - z= - 40

z - x = 40, choice (B).

Click here for the full list of GMAT OG12 explanations.


You should follow me on Twitter. While you're at it, take a moment to subscribe to GMAT Hacks via RSS or Email.

Total GMAT Math

The comprehensive guide to the GMAT Quant section. It's "far and away the best study material available," including over 300 realistic practice questions and more than 500 exercises!
Click to read more.