SOMETHING MAGIC ABOUT SQUARE PUZZLES THEY ARE SIMPLY IRRESISTIBLE. SCIENTIFICALLY PROVEN THAT REGULAR SUDOKU PUZZLE SOLVING IMPROVES IQ AND KEEPS BRAIN IN TOP SHAPE. 500 9x9 SUDOKU PUZZLES WITH SOLUTIONS. DIFFICULTY LEVELS: VERY EASY, EASY, MEDIUM, HARD, BEAST & DEVIL. COMPUTER CAN SOLVE "VERY EASY" SUDOKU PUZZLES IN LESS THAN A SECOND, MEANWHILE "DEVIL" DIFFICULTY LEVEL PUZZLES TOOK AROUND 6 SECONDS. FORMATTED 2 TO A PAGE FOR EASY SOLUTION WORK. EACH PUZZLE WAS CHECKED FOR A SINGLE SOLUTION. IQ CAN BE INCREASED BY STARTING AT A LOW DIFFICULTY LEVEL AND PROCEEDING TOWARD DIFFICULT PUZZLES.