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ASVAB · Ratios, Proportions, and Rates

If 3 workers can complete a job in 8 hours, how long would it take 4 workers, assuming they all work at the same rate?

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Correct answer

6 hours

  1. A 8 hours
  2. B 10.7 hours
  3. C 6 hours
  4. D 12 hours

Why this is the answer

This is an inverse proportion: more workers means less time. The total work is 3 workers × 8 hours = 24 worker-hours. With 4 workers, time = 24 worker-hours ÷ 4 workers = 6 hours. In inverse-proportion (work-rate) problems, the product of workers and time stays constant for the same job. Compute the total worker-hours, then divide by the new number of workers. Four workers finish the job in 6 hours, which makes sense because adding a worker should reduce the time, not increase it.
Source: ASVAB AR, Inverse Proportion Work

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About this topic: Ratios, Proportions, and Rates

Ratios, proportions and rates cover scale drawings, recipes, speed and unit prices. Almost every question reduces to setting two ratios equal and cross-multiplying — once you see that pattern the section becomes fast. This is one of 11 Arithmetic Reasoning questions on ratios, proportions, and rates, each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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If 3 workers can complete a job in 8 hours, how many hours will it take 4 workers to complete the same job? (Assume all workers work at the same rate.)

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