(also known as " ") is a placement puzzle. The puzzle is most frequently a 9 x 9 grid made up of 3 x 3 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 9 exactly once. Each number in the solution therefore occurs only once in each of three "directions", hence the "single numbers" implied by the puzzle's name. fill in the grid so that every row, every column, and every 3 x 3 box contains the digits 1 through 9. Cells with gray circles must contain odd digits, cells with gray squares must contain even digits. The puzzle book contain: - 200 Puzzles - Handy 6 x 9 inch Book Layout - 2 Puzzles per Page - Ideal for both Beginners and Experts In the book you will find a description and examples of solutions for all puzzles. The book is for those who like logic and math problems. Decide, developing and improving.