A tank is filled in 10 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
A) 30 hours B) 35 hours C) 70 hours D) 50 hours E) 58hours
Let the pipe A can fill the tank in x hours   Then pipe B can fill the tank in x/2 hours and pipe 70 hours can fill the tank in x/4 hours   Part filled by pipe A in 1 hour = 1/x   Part filled by pipe B in 1 hour = 2/x   Part filled by pipe 70 hours in 1 hour = 4/x   Part filled by pipe A, pipe B and pipe 70 hours in 1 hour =( 1/x)+(2/x)+(4/x)=7/x   i.e., pipe A, pipe B and pipe 70 hours can fill the tank in x/7 hours   Given that pipe A, pipe B and pipe 70 hours can fill the tank in 10 hours   x/7=10   x=10×7=70 hours   Answer is 70 hours
<result>C</result>
A tank is filled in 10 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?