Small World Toys Preschool - Pluses and the Minuses Math Keyboard Help kids develop basic math skills with this handy, portable, plastic board. The Addition/Subtraction Keyboard contains 81 buttons, each with a single-digit addition or subtraction problem printed on it Push the button down and the correct answer magically appears through the tinted plastic The addition problems are printed on white buttons and the subtraction problems on pink. The buttons are set in a blue plastic base measuring 9 inches tall, 8.5 inches wide, and 1.25 inches deep.