If 5 workers take 8 hours to complete a job, how long would 10 workers take, assuming the same rate?

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Multiple Choice

If 5 workers take 8 hours to complete a job, how long would 10 workers take, assuming the same rate?

The key idea is that total work is fixed and the time needed scales inversely with the number of workers, assuming each worker’s rate stays the same. Five workers take eight hours, so the job requires 5 × 8 = 40 worker-hours of effort. With ten workers, the same 40 worker-hours can be completed in 40 ÷ 10 = 4 hours. Doubling the workforce halves the time when each person works at the same rate. So the answer is 4 hours.

The key idea is that total work is fixed and the time needed scales inversely with the number of workers, assuming each worker’s rate stays the same. Five workers take eight hours, so the job requires 5 × 8 = 40 worker-hours of effort. With ten workers, the same 40 worker-hours can be completed in 40 ÷ 10 = 4 hours. Doubling the workforce halves the time when each person works at the same rate. So the answer is 4 hours.

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