Pipes and Cistern - General Aptitude

Q1:

A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

A 20 hours

B 25 hours

C 35 hours

D Cannot be determined

E None of these

ANS:C - 35 hours

Suppose pipe A alone takes x hours to fill the tank.

Then, pipes B and C will take x and x hours respectively to fill the tank.
2 4
1 + 2 + 4 = 1
x x x 5
7 = 1
x 5
x = 35 hrs.