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## Official Guide Explanation:

Problem Solving #21

**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****: 21**

Page: 64

Difficulty: **5** (Moderate)

Category 1: Geometry > Coordinate Geometry > Slope

Category 2: Geometry > Coordinate Geometry > Other

**Explanation:** (A) and (B) are the equations for the axes, and since the shaded region is bounded by the axes on the left and bottom, those two choices are eliminated. x = 1 is the boundary on the right side: vertical lines are always x= an integer. It isn't nearly as obvious what the equation of the diagonal line is, but it may be clearer that (D) isn't it. x - y = 0 is the same as x = y, and x = y is a diagonal line that goes through the origin (when x = 0 and y = 0) and moves up and to the right from there. Thus, (D) is the odd man out, and the correct answer.

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