A man can do a certain task in 21 hours, another can do the task in 28 hours, and a boy can do the task in 48 hours. How long will it take to do the task if all work together?
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Every hour man 1 does of the job, man 2 does of the job, and the boy does of it. So that means, every hour of the job gets done . So if we set up a ratio (amount of job : hours)... . So they will finish the job in hours, or 9 hours 36 mins.
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