I sometimes do math (mostly algebra) that many would consider unnecessary, but it can be fun! For instance, do you think that if all students at the University of Puget Sound paid their tuition in pennies, it would fill up the dining hall in the SUB? All you need are some dimensions (bricks, pennies, floor tiles, etc.) and you can get a rough estimate. Or how much does it actually cost to skip class? My fun math category is dedicated to math like that.