To fill a cistern, pipes P, Q & R take 20, 15 & 12 minutes respectively. The time in minutes that the three pipes together will take to fill the cistern is:__________?
Q1. To fill a cistern, pipes P, Q & R take 20, 15 & 12 minutes respectively. The time in minutes that the three pipes together will take to fill the cistern is:__________?
Answer: 5 min
Explanation: Combined rate = 1/20 + 1/15 + 1/12 = 3/60 + 4/60 + 5/60 = 12/60 = 1/5; cistern fills in 5 minutes.