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?  Choose the correct choice from the following options:  A) 77 hrs  B) 81 hrs  C) 35 hrs  D) 17 hrs  E) 19 hrs
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?