A tank is filled by 3 pipes A,B,C in 10 hours. Pipe C is twice as fast as B and B is twice as fast as A. How much will pipe A alone take to fill the tank ?	Pick.
A) 20hr  B) 52hr  C) 70hr  D) 66hr  E) 48hr
Suppose pipe A alone take x hours to fill the tank   Then pipe B and C will take x/2 and x/4 hours respectively to fill the tank.   1/x + 2/x + 4/x = 1/10   7/x = 1/10   x = 70 hours   Answer is 70hr
<result>C</result>
A tank is filled by 3 pipes A,B,C in 10 hours. Pipe C is twice as fast as B and B is twice as fast as A. How much will pipe A alone take to fill the tank ?