# Pipes & Cistern Practice Question

This aptitude practice question helps understand the basics of how problems in pipes and cisterns should be solved. The rate at which a pipe fills a tank is usually provided in terms of the time taken by a pipe to fill the tank. Therefore, the rate at which it fills is computed as a fraction of the tank that gets filled in unit time. These questions are commonly classified as word problems in GMAT and GRE as solving these questions entail framing mathematical expressions and equations from information given in words. An easy to medium level difficulty question.

## Question

A tank is fitted with 8 pipes, some of which that fill the tank and others that empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of those that empty the tank empties it in 6 hours. If all the pipes are kept open when the tank is full, it will take 6 hours to drain the tank. How many of these are fill pipes?

1. 2 fill pipes
2. 4 fill pipes
3. 6 fill pipes
4. 5 fill pipes

Correct Answer      Choice (2). 4 of the 8 pipes are fill pipes .

• #### Words to Mathematical Expressions and Equations

Let the number of fill pipes be 'n'
Therefore, there will be (8 - n) waste pipes.

Each of the fill pipes can fill the tank in 8 hours.

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