Three pipes A, B and C can fill a cistern in 12, 16 and 24 minutes respectively. All the pipes are opened together but 3 minutes before the cistern is full pipe C stop working. How much time will the cistern take to fill?

06 min

If pipe C also works for the last 3 min, then extra work could be done = 2 × 3 ⇒ 6

Total work would be = 48 + 6 = 54, when all three pipes working all the time.

Total time ⇒ \(\frac{54}{(4 + 3 + 2)}\) ⇒ \(\frac{54}{9}\) = 6 Mins. = Total time taken by all three according to the condition given in the question.