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Official Guide Explanation:Problem Solving #102

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: 102
Page: 74
Difficulty: 5 (Moderate)
Category 1: Geometry > Coordinate Geometry > Slope

Explanation: The equation of a line is y = mx + b, and we're given m = 2. We know the line goes through the origin, (0,0), so we can plug in those values for x and y to find the value of b:

0 = 2(0) + b

b = 0

So the equation of the line is y = 2x.

Given the equation, we can solve for the values of x and y in the two points. The point (3,y) is:

y = 2(3) = 6, so y = 6

The point (x,4) is:

4 = 2x, so x = 2

x + y = 2 + 6 = 8, choice (C).

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