Official Guide Explanation:
Problem Solving #80




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Solution and Metadata

Question: 80
Page: 163
Difficulty: 5 (Moderate)
Category 1: Word Problems > Work Problems > 2 inputs
Category 2: Arithmetic > Ratio and Proportion >

Explanation: First, find the rate of each machine. A operates at 120 bolts per 40 seconds, or ((120b)/(40s)) = 3((b)/(s)). B operates at 100 bolts per 20 seconds, or ((100b)/(20s)) = 5((b)/(s)). Working together, their cumulative rate is 8((b)/(s)), so they will produce 200 bolts in (200/8) = 25 seconds, choice (B).

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