Official Guide Explanation:
Data Sufficiency #28




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: 28
Page: 275
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Descriptive Statistics > Average
Category 2: Word Problems > Other >

Explanation: To find the average salary of all the employees in Q, we'll need to know more than just the number and salary of employees in Division R.

Statement (1) is insufficient. There's no information about the number of employees in Q who are not in R, or about the salaries of those people.

Statement (2) is also insufficient. We don't know anything about the salary of those in Division R, or the number of employees who are NOT in Division R.

Taken together, the statements are insufficient. If we had enough information, we'd set up a weighted average problem like this, where r is the number of employees in R and q is the number of employees in Q who are not in R:

((30,000r + 35,000q)/(r + q)) =

We know that r = 1,000, but we don't know q. Without that number, we can't solve. Choice (E) 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.