Question

Three pipes A, B and C can fill a tank in 9 hours. After working at it together for 3 hours, C is closed and A and B can fill the remaining part in 12 hours. The number of hours taken by C alone to fill the tank is ____.

• A. 16 Hours
• B. 18 Hours
• C. 11 Hours
• D. 09 Hours

Hint:

Use the given age ratio five years from now to set up an equation in the son's age.

Answer 1

The Correct Option is B

Pipes A, B and C together fill the tank at a rate of \(1/9\) of the tank per hour. Working together for 3 hours fills \(3 \times 1/9 = 1/3\) of the tank, leaving \(2/3\) still to be filled.
That remaining \(2/3\) gets filled by A and B alone in 12 hours, so their combined rate is \(\dfrac{2/3}{12} = \dfrac{1}{18}\) per hour.
C's individual rate is then \(1/9 - 1/18 = 1/18\), which means C alone would take 18 hours to fill the tank, matching option 2.