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1. A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

A. 20 hours

B. 25 hours

C. 35 hours

D. Cannot be determined

Solution:

Suppose pipe A alone takes x hours to fill the tank.
Then, pipes B and C will take

\frac{x}{2}

and

\frac{x}{4}

hours respectively to fill the tank.

\begin{aligned} ∴ \frac{1}{x} + \frac{2}{x} + \frac{4}{x} = \frac{1}{5} \\ \Rightarrow \frac{7}{x} = \frac{1}{5} \\ \Rightarrow x = 35 hours \end{aligned}

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