Our fun-to-use machines make math so simple, kids can teach themselves! Children just press the equation buttons--and up pop the answers. This hands-on approach to basic math operations helps reinforce addition, subtraction, multiplication and division facts through self-checking practice. 81 equation buttons are locked securely into each tough, 8 1/2" x 9 1/2" plastic frame. Complete set includes all 4 math machines. Individual math machines are also available separately.