Put your brain through it's paces with this Brain Gym book of 600 Sudoku puzzles, containing 300 hard and 300 very hard difficulty. We exercise our bodies but our brains need a workout too Sudoku helps keep your brain healthy and functioning well. Challenge yourself to finish all the puzzles without cheating Solutions are printed at the end of the book. 4 puzzles per page. 8.5 by 11".