Official Guide Explanation:
Data Sufficiency #33

Background

This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Quantitative Review (2nd 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: 33
Page: 155
Difficulty: 4 (Moderately Easy)
Category 1: Algebra > Linear Equations-Two Unk >
Category 2: Arithmetic > Percents > other

Explanation: The question gives us an equation: n + m + b = 720. To find n, we'll need a lot more information.

Statement (1) is insufficient. It gives us another equation: m = 0.8b. So far, we have two equations but three variables. There's no way to combine them to isolate n, so we'll have to wait for more information.

Statement (2) is sufficient. The equation here is: n = 0.6(m + b). Note what happens. While the question separates magainzes and books, (m + b) appears in this equation and the equation in the question stem. If we reduce the question to "newspapers" and "non - newspapers," (call those z) here are the equations:

n + z = 720

n = 0.6z

Two equations, two variables. That's enough information, and choice (B) is correct.

Click here for the full list of GMAT Quant Review explanations.

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.