Three pipes A, B, and C fill a tank together in 5 hours. Pipe C fills the tank at twice the rate of pipe B, and pipe B fills it at twice the rate of pipe A. How long will pipe A take to fill the tank by itself?

Explanation

Let the time taken by pipe A alone to fill the tank be x hours. Since pipe B is twice as fast as A, it will take x/2 hours, and pipe C, being twice as fast as B, will take x/4 hours. Their combined filling rates add up as: 1/x + 1/(x/2) + 1/(x/4) = 1/5. Simplifying, 1/x + 2/x + 4/x = 1/5, which is 7/x = 1/5, leading to x = 35 hours. Therefore, pipe A alone requires 35 hours to fill the tank.