This series have four different levels: easy, normal, hard, and expert. This book is normal level. if you need other level, please check "Mike Murphy Sudoku." Sudoku keep your brain logical thinking, even at a young age. Sudoku improves critical thinking and making quick decisions based upon available evidence. Sudoku is not only fun and interesting. It is a brain game that helps to train the brain of you and your child. Sudoku also demands attention to detail - noticing patterns, and finding the right moment to make a move. How to play? The goal of Sudoku is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 to 9 exactly once. Sudoku normal level vol.1 Details - Small Print (5x8) to easy take with - 100 Normal Level Sudoku Puzzles Collection - You can challenge yourself by writing down the time, you used. Enjoy!