Official Guide Explanation:
Data Sufficiency #158




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: 158
Page: 287
Difficulty: 5 (Moderate)
Category 1: Word Problems > Rate Problems > other
Category 2: Arithmetic > Ratio and Proportion >

Explanation: Statement (1) is sufficient: if each member contributes $4 and the total contribution is $60, the number of members is (60/4) = 15.

Statement (2) is trickier, but also sufficient. Say that the number of members is m and the contribution per member is c. Thus, the contribution per person is given by (60/(m)) = c. However, if 5 members fail to contribute, the number of contributing members is m - 5, and the contribution is c + 2. Thus, (60/(m - 5)) = c + 2. That's two linear equations with two variables. They would take some time to solve, but luckily you don't have to. Choice (D) is correct.

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.