Alberto and Benito are two brothers who share a room. Alberto is a very careful child who likes to have everything well organized. He is able to tidy up his room in just two hours. Benito however, is a very carefree child who leaves things in any way and is able to mess up the room in three hours.
One day the two met in the room with everything upside down and while Alberto began to order Benito dedicated himself to undoing order.
How long did Alberto take to tidy the room?
In six hours Alberto is able to order three rooms and in that same time Benito can mess up two. So that, in six hours the room was tidy.