The book contains 400 excellent Killer Sudoku puzzles 9x9 at the level of Hard. All riddles have only 1 solution. 2 puzzles per page. The font size is correct you will not have to strain your eyes when solving puzzles. High quality paper and print (all puzzles read well, easy to write with pen and pencil without worry of bleed-through). Killer Sudoku is based on the original Sudoku grid, with the same rules and numbers-1 to 9, but with an added mathematical challenge. The only difference is the killer Sudoku: additional numbers are given - the sums of values in groups of cells. The numbers contained in the group cannot be repeated. This variant also called "Sums Sudoku", "Sums Number Place", " Samunamupure ", "Kikagaku Nampure".