Pipe A can fill an empty tank in 10 h, Pipe B can fill the same tank, when empty, in 15 h, and Pipe C can empty the same tank, when completely full, in 12 h. Find the time taken to fill half the tank if all three pipes are opened simultaneously when the tank is empty.

6 h

A+ = 10 hours, B+ = 15 hours, C- = 12 hours,

⇒ Time required by A + B + C to fill half the tank = \(\frac{60/2}{6+4-5}\) = \(\frac{30}{5}\) = 6 hours