I once taught private lessons in math on calculating the area of a circle and I wanted to show the students how much cheaper per area a larger pizza is. So we of course got the diameters of pizzas from their favorite restaurant and started calculating. Then we found out that the normal sized pizza was actually the cheapest per area. It wasn‘t quite what we expected, but a very good math lesson for the attendees nonetheless: The owner lost money, because they were bad at maths.