# CAT Practice : Pipes cisterns, Work time

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Sum of the rate of flow of individual pipes gives the combined flow rate

## Pipe flow rate

Q.11: Pipe A can fill a tank in 12 hours. When it works along with Pipe B, it can fill the tank in 8 hours. In how many hours can pipe B fill the same tank independently?.
1. 8 hrs
2. 12 hrs
3. 24 hrs
4. 16 hrs

Choice C. 24 hrs

## Detailed Solution

Let the capacity of the tank be C.
Rate of Pipe A = $\frac{C}{A}$
Rate of Pipe B = $\frac{C}{B}$
Rate of Pipe A and Pipe B together = $\frac{C}{A} + \frac{C}{B} = \frac{C}{8}$
$\frac{C}{12} + \frac{C}{B} = \frac{C}{8}$
$\frac{C}{B} = \frac{C}{8} - \frac{C}{12} = \frac{C}{24}$

Pipe B independently will take 24 hours to fill the tank.

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## More questions from Pipes Cisterns, Work Time

Mathematicians are creatures of habit. This topic has been called Pipes and Cisterns because someone named it like it long ago. Pipes and Tanks would be much better - at least makes it sound like wartime.