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 hours and each outlet pipe can empty the tank in 6 hours. On opening all the pipes, an empty tank is filled in 9 hours. The number of inlet pipes is
Total number of pipes = 6 (given)
Let number of inlet pipes = x
∴ number of outlet pipes = 6 –x
Now, Inlet pipe fill the tank in 9 hours and outlet pipe empty it in 6 hours.
∴ Total part filled in 1 hour
=
When all the pipes are opened.
But given total part filled in 9 hr
∴
⇒ 15x = 60 ⇒ x = 4
Hence, number of inlet pipes = 4.