Official Guide Explanation:
Problem Solving #158




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: 158
Page: 83
Difficulty: 5 (Moderate)
Category 1: Algebra > Functions > Sequences

Explanation: The rule says that for any number in the set, a number 2 greater than itself must also be in the set. Note that this works in only one direction. Since we know that -1 is in the set, we know that (-1 + 2) = 1 is also in the set. All odd numbers above that--3, 5, 7, etc.--are in the set as well. However, -3 is not necessarily in the set. We only know that -1 and all positive odds are present. Thus, roman numeral I need not be true, while II and III are true. Choice (D) is correct.

Click here for the full list of GMAT Quant Review 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.