Official Guide Explanation:
Problem Solving #122

 

 

Background

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.

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Solution and Metadata

Question: 122
Page: 169
Difficulty: 6 (Moderately Difficult)
Category 1: Algebra > Symbolism >
Category 2: Arithmetic > Fractions >

Explanation: If a θ c = 0, then we can substitute a and c for a and b in the expression ((a - b)/(a + b)). That gives us ((a - c)/(a + c)) = 0. The only way for a fraction to be equal to zero is if the numerator is equal to zero, so a - c = 0. Since we're interested in c, isolate it on one side: c = a, choice (E).

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