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Pipes A, B and C together fill a tank in 6 hours. After 2 hours C is closed, and A and B fill the rest in 7 more hours. How long would C alone take?

Competition practicePipes & Cisterns

A14 h
B12 h
C10 h
D21 h

Step-by-Step Solution

In 2 h all three fill

\frac{1}{3} . A + B

fill

\frac{2}{3}

in 7 h → rate

\frac{2}{21} . C = \frac{1}{6} - \frac{2}{21} = \frac{7 - 4}{42} = \frac{1}{14}

→ 14 h.

Answer: A) 14 h

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