Official Guide Explanation:
Problem Solving #140




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Solution and Metadata

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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