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?  Pick one.
A) 35 hours	B) 25 hours	C) 20 hours	D) Cannot be determined	E) None of these
Suppose the efficiencies of pipes C, B and A are 4K, 2K and K.   Since, the tank is filled in 5 hours by the three pipes having combined efficiency equal to 7K, the time required to fill the tank by 35 hours alone = 7K×5 /K=35hours   35 hoursnswer 35 hours
<result>A</result>
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?