### Bookshelf

 Total GMAT Math Jeff's complete Quant guide, on sale now!
 Total GMAT Verbal Everything you need to ace GMAT Verbal!
 New: GMAT 111 Improve every aspect of your GMAT prep!

Guides To the Official Guide
(Updated for new editions!)

1,800 Practice Quant Questions

GMAT Question of the Day

GMAT Official Guide
OG Math | OG Verbal

Beginner's Guide to the GMAT

GMAT Hacks Affiliate Program

### Resources

MBA.com
GMAC Official Site
Free GMATPrep Practice Tests

Stacy Blackman Consulting
Book | Essay Guides

GRE HQ
Total GRE Math

Ultimate SAT Verbal

## Official Guide Explanation:Data Sufficiency #1

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.

Question: 1
Page: 153
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Descriptive Statistics > Average
Category 2: Algebra > Linear Equations-Two Unk >

Explanation: To find the average of x and y, we simply need the sum of x and y. (To find the average, we'd divide by 2, but for Data Sufficiency, we don't need the exact average.)

Statement (1) is insufficient. It tells us that ((x + 2y)/2) = 10. There's no way to get from there to the value of x + y.

Statement (2) is also insufficient. This one tells us that ((2x + 7y)/2) = 32. Again, no way to get to x + y from there.

Taken together, the statements are sufficient. We can simplify the equations from each of the statements to get the equations:

x + 2y = 20 and

2x + 7y = 64

Those are two linear equations with two variables. No need to solve, just recognize that we can. Choice (C) is correct.

 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.