Back in kindergarten (yes, I remember because this was my first time feeling the need to truly facepalm), 3 of my classmates (we were seated in groups of four) argued with me that 30+30=60. I had them write and solve 3+3. I then added the zeroes into the completed equation. They argued that it didn't work that way. I then showed them with a calculator. Still didn't believe me. We asked the teacher. They said she was wrong too I wanted to facepalm so -blam!-ing hard. Edit: they were trying to argue that 30+30=80