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## Official Guide Explanation:Problem Solving #99

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: 99
Page: 74
Difficulty: 5 (Moderate)
Category 1: Algebra > Simplifying Algebraic Expressions >
Category 2: Algebra > Equations >

Explanation: You could try to rearrange the equation a + b = c to make it look like one of the five answer choices, but it's probably faster to assign values to each of the variables and test them in the answer choices. Say a = 2, b = 3, and c = 5. Those satisfy the initial equation. Check to see which of the answer choices is equal to 1 with those numbers:

(A) ((a - b)/(c)) = ((2 - 3)/5) = ((-1)/5)= - (1/5)

(B) ((a - c)/(b)) = ((2 - 5)/3) = ((-3)/3)= - 1

(C) ((b - c)/(a)) = ((3 - 5)/2) = ((-2)/2)= - 1

(D) ((b - a)/(c)) = ((3 - 2)/5) = (1/5)

(E) ((c - b)/(a)) = ((5 - 3)/2) = (2/2) = 2. That's it.

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