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All three pipes in the figure are opened on the empty tank. How long will it take to fill?

Competition practicePipes & Cisterns

A $3 \frac{3}{7} h$
B6 h
C4.8 h
D $2 \frac{2}{3} h$

Step-by-Step Solution

Per hour:

\frac{1}{6} + \frac{1}{8} - \frac{1}{12} = \frac{4 + 3 - 2}{24} = \frac{5}{24}

→

\frac{24}{5} = 4.8

h

. (3 \frac{3}{7}

h ignores the outlet;

2 \frac{2}{3}

h counts it as an inlet.)

Answer: C) 4.8 h

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