it’s not as difficult as it first looks:
Given two water faucets, one hot and one cold, and one bucket. The hot water fills the empty bucket in eight minutes. The cold water fills the bucket in seven minutes. Then I make a hole in the bucket such that the full bucket drains in four minutes. Now take the empty bucket, with the hole, and place under both faucets together. Turn on the hot and cold water at the same time. How long does it take to fill the bucket halfway?