A tank is filled by 3 pipes A,B,C in 7 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 ? Choices:	A) 25hr	B) 35hr	C) 40hr	D) 49hr	E) 50hr
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 = 1/7   7/x = 1/7   x = 49 hours   Answer is 49hr
<result>D</result>
A tank is filled by 3 pipes A,B,C in 7 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 ?