Question 968957
Two pipes fill a storage tank in 9 hours. The larger pipe fills the tank three times as fast as the smaller one. How long would it take the larger pipe to fill the tank alone?
let smaller pipe take  3x hrs to fill the tank and big take x hours 
big one hours =1/x and other 1 hours =1/3x
both pipe together in 1 hours = 1/x+1/3x=4/3x hours 
as per given conditions both pipe  fill up tank in 1 hours =1/9
4/3x=1/9  by cross multiplication 
36=3x
X=12 hours 
answer 12 hours