Question

Six pipes are fitted to a water tank. Some of these are inlet pipes and the others outlet pipes. Each inlet pipe can fill the tank in 9 h and each outlet pipe can empty the tank in 6 h. On opening all the pipes, an empty tank is filled in 9 h. The number of inlet pipes is

• A. 4
• B. 3
• C. 2
• D. 5

Answer 1

Answer: (A)

4

Answer 2

Let there are x inlet pipes.

work done by inlet $=\frac{1}{9}$

work done by outlet $=\frac{1}{6}$

Here 6-x is the outlets

$\frac{x}{9}-\frac{(6-x)}{6}=\frac{1}{9}$

5x=20
x=4
Then there will be 4 inlet pipes the will to fill the tank.
So the correct option is (A)