DUCTION: This game is a test and practice of your calculating ability. Your mission is simple: select numbers and operations to make a correct expression! For example: Correct expression: 13 + 5 -4 + 12: 2-4 x 3 = 8. Wrong expression: 13 + 5 -4 + 12: 2-4 x 3 = 7. RULES: You choose numbers and operations on the screen. Each numbering position can only be selected once.