Out of three pipes the first two can fill an empty tank in 9 and 18 hours, respectively while the third can drain the filled tank in 15 hours. If all the three pipes are opened when the tank is empty, after how many hours will the tank be full?
n 1 hour pipe A will fill $$\frac{1}{9}$$th of the tank.
In 1 hour pipe B will fill $$\frac{1}{18}$$th of the tank.
In 1 hour pipe C will empty $$\frac{1}{15}$$th of the tank.
So in 1 hour, total
$$\frac{1}{9}+\frac{1}{18}-\frac{1}{15}$$ Â = $$\frac{10+5-6}{90}$$ = Â part is full in 1 hour.
So in 10 hours , the tank will be full.
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