Problema Solution

An empty oil tank can be filled by a pipeline in 10 hours. The tank can be emptied in 20 hours by opening a valve. If the valve is opened while the pipeline is filling the tank, how long will it take for the tank to fill?

Answer provided by our tutors

the rate of the pipeline is 1/10 tank per hour


the rate of the valve is 1/20 tank per hour


let 't' the time needed for the tank to fill


t(1/10 - 1/20) = 1


by solving we find:


t = 20 hr


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it will take 20 hours for the tank to fill.