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) 20 hours  B) 25 hours  C) 35 hours  D) Cannot be determined  E) None of these
If c takes x hrs, B takes 2x hrs and A takes 4x hrs,   then   1/x +1/2x = 1/4x = 1/5   7/4x = 1/5   x= 7*5/4 hrs = 35/4 hrs   So A alone will take  4*35/4= 
<gadget id="calculator"> 4*35/4</gadget>
<output>35</output>
35 hrs   ANSWER:35 hours
<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?