A tank is filled in 4 hours by three pipes A, B and C. The pipe C is twice as fast as B and pipe B is thrice as fast as A. How much time will pipe A alone take to fill the tank?

40 hours

A + B + C = 4 hrs,

The pipe C is twice as fast as B and pipe B is thrice as fast as A. therefore,

A : B : C = 1 : 3 : 6  (Efficiency)

⇒ Total capacity = (1 + 3 + 6) x 4 = 10 x 4 = 40 hrs,

⇒ Time required by A to completely fill the cistern alone = \(\frac{40}{1}\) = 40 hours.