OutNumbered! is a side-scrolling educational game whose objective is to stop the Master of Mischief, a common antagonist of The Learning Company's Super Solvers series and Treasure series, from taking over a television and radio station before midnight. To do this, the player must deduce which room the Master of Mischief is hiding in by comparing sets of patterns for each room to those of the room the Master of Mischief is hiding in. To obtain the pattern for each room, the player must visit each room and solve a math puzzle related to that room.
During the course of the game, the player will randomly happen upon the Master of Mischief's robot, Telly. Telly will attempt to knock down the player by either crashing into him or hitting him with hurled discs. If the player zaps Telly with his zapper before either of these things happen, he will get a chance to earn a clue to the pattern of the room that the Master of Mischief is hiding in.
When the player has all four patterns for the room the Master of Mischief is hiding in as well as those of each room, he must decide which room he thinks the Master of Mischief is hiding in. The player must compare clues obtained by zapping Telly to those for each room. If the player correctly guesses the room the Master of Mischief is hiding in, he will get a bonus score based on time and zapper energy remaining. This score will then be added to the player's lifetime score. If the guess is incorrect or the player fails to gather enough information by midnight, he will lose the game and his lifetime score will not change.
As the player wins more games, his lifetime score will increase. At certain score amounts, the player will advance in rank and the game becomes more difficult.