One inlet pipe can fill an empty pool in 6 hours, and a drain can empty the pool in 12 hours. How long will it take the pipe to fill the pool if the drain is left open?

Answer 1

So every hour one pipe fills 1/6 of the goal and the other drains 1/12 of the pool so the net gain is 1/12 every hour. at that rate the pol will be filled in 12 hours