Find X Mathematic Coaster Set - Ceramic Tile 4 Piece Set - Caddy Included

We have never understood why math teachers are so fascinated by the letter X, when there are at least 25 other perfectly good letters they could use (even before resorting to the Greek alphabet). Neither have we understood why they are always losing X, nor why they seem to be incapable of finding it themselves and must resort to asking their students, who couldn't care less about the location of X, or any other random letter.