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?
Select the correct option
A) 20 hrs  B) 25 hrs  C) 35 hrs  D) Cannot be determined  E) None of these
Suppose pipe A alone takes x hours to fill the tank.   Then, pipes B and C will take x/2 and x/4 hours respectively to fill the tank.   1/x + 2/x + 4/x = 1/5   7/x = 1/5 =&gt; x = 35 hrs.   ANSWER:35 hrs
<result>C</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?