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All three pipes in the figure are opened together on an empty tank. In how many hours will it be full?

Competition practicePipes & Cisterns

A7.5 h
B6 h
C5 h
D10 h

Step-by-Step Solution

Per hour:

\frac{1}{10} + \frac{1}{15} - \frac{1}{30} = \frac{3 + 2 - 1}{30} = \frac{4}{30}

. Time =

\frac{30}{4} = 7.5

h. (6 h ignores the outlet C.)

Answer: A) 7.5 h

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