# CAT Practice : Pipes cisterns, Work time

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Classic Pipes - Cisterns Question!!

## Pipes

Q.16: A cistern of capacity 40 litres has an inlet and an outlet pipe. When both the pipes are opened at once, it takes 8 minutes to fill the cistern. However, if the outflow rate is increased 1.5 times, the cistern never gets filled. Which of the following can be the outflow rate?
1. 8 litres/minute
2. 6 litres/minute
3. 12 litres/minute
4. 9 litres/minute

Choice C. 12 litres/minute

## Detailed Solution

Initially, net flow in the tank = 40 litres/ 8 minutes = 5 litres/minute

Now, the increase in outflow should be greater than 5 litres/min for the tank to fill up

Increase in outflow = 1.5x – x = 0.5x

Only in option c) 0.5 X 12 = 6 litres/min > 5 litres/min

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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.