Mystery Numbers is a fun, interactive game played with at least two people—one “detective,” or guesser, and another player who comes up with the “mystery number.” You could also try this game with two teams. For the first few rounds, you might need to explain how to solve for the mystery number using algebra, although you don’t have to use letters. We love this game because it’s so versatile—you can use it for any grade and with students at different levels of math development, depending on which mathematical operations are included. When used as extra practice after a lesson or as a warm-up activity at the start of a class, this game helps establish big picture essential understandings around operations and develops students’ algebraic skills. Good luck, detectives!