It takes 7 people 5 minutes to paint 3 walls. How long will it take 5 people to paint 2 walls?
Assuming all people work at the same speed, it takes 4 minutes and 40 seconds to accomplish this task.
There are two fundamental changes to this problem between the two scenarios- the number of people and the number of walls.
The number of people you have working on the walls is inversely proportional to the amount of time it takes- the more people, the less time it takes.
The number of walls is directly proportional- the less walls, the less time it takes.
7 people take 5 minutes to paint 3 walls.
Those 7 people would take 1 minute and 40 seconds (1/3 of 5 minutes) to paint 1 wall.
Furthermore, it would take them 3 minutes and 20 seconds to paint 2 walls by this same logic.
1 person would take 23 minutes and 20 seconds to paint 2 walls. This is 7 times longer than 7 people would take to complete this task.
5 people would take 1/5 of the time that the 1 person would, and 23 minutes and 20 seconds divided by 5 is 4 minutes and 40 seconds.
5 people would take 4 minutes and 40 seconds to paint 2 walls.