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## Official Guide Explanation:Problem Solving #140

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: 140
Page: 80
Difficulty: 6 (Moderately Difficult)
Category 1: Word Problems > Work Problems > 2 inputs
Category 2: Algebra > Linear Equations-One Unk >

Explanation: The amount of time it takes two machines to complete a job working together is given by ((AB)/(A + B)), where A and B are the times required for each individual machine to do the job. In this case, A = 5, B = x, and the result is 2. The equation, then, looks like this:

((5x)/(5 + x)) = 2

5x = 2(5 + x)

5x = 10 + 2x

3x = 10

x = (10/3) = 3(1/3), choice (A).

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