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With the inlet and the leak in the figure both open, how long does the empty tank take to fill?

Competition practicePipes & Cisterns

A $6 \frac{2}{3} h$
B4 h
C15 h
D25 h

Step-by-Step Solution

Net

= \frac{1}{5} - \frac{1}{20} = \frac{3}{20}

per hour →

\frac{20}{3} = 6 \frac{2}{3}

h. (4 h treats the leak as another inlet.)

Answer: A)

6 \frac{2}{3} h

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