We all remember the people who would do mental math in class all the time. You know, those kids who thought it was cool that they could do double-digit multiplication in their heads. Sure, it could make them seem intelligent, and perhaps they are. But it also makes you straight-up obnoxious, and in some cases (like this one), your work can be straight-up wrong. Not to take us down a mathematics rabbit hole, but do any of us remember that point when algebra became hard? That point of no return w…