Do you Sudoku? This addictive logic-based game from Japan involves numbers, and sharpens your concentration and reasoning, but requires no mathematical skills to play. Filled with 200 grids of varying difficulty (100 beginner, 75 easy, and 25 medium), our pocket-sized hardcover notepads include a pencil and are perfect for strategizing on the bus or train. Now that's what we call a smart calculation!