Pipe A and B can empty a full tank in 18 hours and 24 hours,respectively. Pipe C alone can fill the tank in 36 hours. If the tank is $\frac{5}{6}$ full and all the three pipes are opened together, then in how many hours will the tank be emptied?

12

A- = 18 hrs, B - 24 hrs, C+ = 36 hrs,

⇒ \(\frac{5}{6}\) of total capacity = \(\frac{5}{6}\) x 72 = 60 units,

⇒ Time required by A + B + C to empty 60 units of the tank = \(\frac{60}{-4-3+2}\) = \(\frac{60}{5}\) = 12 hours.