A delightful collection of 150 brain challenging puzzles, from easy to more difficult levels: Sudoku Puzzles – easy Sudoku Puzzles – Moderate Sudoku Puzzles – Moderately Hard Sudoku Puzzles – Hard Killer Sudoku PuzzlesThis collection is ideal for the whole family. While you are having fun solving the puzzles, your brain is being exercised, too. This helps to improve memory, logic skills, and concentration.