Medium
A water tank has three taps A, B and C. Tap A alone fills the tank in 4 hours, tap B alone fills it in 6 hours, and tap C alone empties it in 3 hours. How long will it take to fill the tank if all three are opened together?
Explanation
Explanation
Rate of A = 1/4 (filling), B = 1/6 (filling), C = 1/3 (emptying). Net rate = 1/4 + 1/6 − 1/3 = 3/12 + 2/12 − 4/12 = 1/12. Therefore, the tank will fill in 12 hours.
PRO TIP
Re-check your working by substituting the answer back into the original question.