I saw a mysterious picture on an electronic whiteboard in a school I was walking past. I couldn't hear what the teacher was saying, but I could see on the timetable that it said 'Maths'. Can you work out what the lesson was about?
I believe this is the rearrangement inequality, perhaps with coin values.
The rearrangement inequality is essentially saying that if you have two sets of positive numbers of the same size, and you pair one from each set with one from the other, take their products and sum, the greatest sum you can get is when you pair the greatest with the greatest, the least with the least, etc., and the lowest sum you can get is when you do the exact opposite.
Here, our sets are [2,3,5] and [20,50,100]. Green light represents the max, red light represents the min. The reason why the rest are yellow is because you can't work out how they are ordered without knowing the specific numbers in the sets.