Who is asking: Student
Al washes a car in six hours. Fred washes a car in eight hours. How long will it take them to wash a car together?
Eight hours to wash a car! Is it a railroad car?
The way to look at this problem is to consider the rate at which each of them washes a car. Al washes at one eighth of a car per hour and Fred at one sixth of a car per hour. Thus together they wash at (1/6 + 1/8) = 7/24 of a car per hour. Hence to wash one car they would have to work 24/7 or 3 4/7 hours.
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