Count work done in one hour
A and B each finish one job alone in 4 hours. Both work at steady rates without slowing each other down.
Each completes 1/4 job per hour. Together: 1/4 + 1/4 = 1/2 job per hour. One job takes 1 ÷ (1/2) = 2 hours.
Combine unequal rates
A finishes one job alone in 3 hours; B takes 6 hours. They work together at steady rates without slowing each other down.
Their rates add: 1/3 + 1/6 = 1/2 job per hour. One job takes 1 ÷ (1/2) = 2 hours.
Try two equal workers
A and B each take 6 hours to finish one job alone. They start together and work at steady rates without slowing each other down.
Find each worker’s fraction of a job per hour. Add the rates, then divide one whole job by that total.
Try it
A and B each need 6 hours alone. At steady rates without slowing each other down, how long do they need together for one job?
- 3 h
- 12 h
Show the answer
3 h
Yes. 1/6 + 1/6 = 1/3 job per hour. One job takes 1 ÷ (1/3) = 3 hours.
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Practice Speed & work rates