If 5 workers complete a job in 10 hours, how many hours would 2 workers need to complete the same job?

• A. 25
• B. 20
• C. 12
• D. 30

Answer: (A)

The situation relies on the idea that total work is fixed and all workers contribute at about the same rate, so time and number of workers are inversely related.

First, find the total amount of work in worker-hours: 5 workers × 10 hours = 50 worker-hours. With 2 workers, the time needed is 50 worker-hours ÷ 2 workers = 25 hours. So the job would take 25 hours.

Other times don’t fit because they would require a different total amount of work or a different number of workers to keep the same rate, which isn’t the case here. Only 25 hours preserves the constant 50 worker-hours of work with 2 workers.