The book contains 400 excellent Binary puzzles 9x9. Easy puzzles 200 Medium puzzles 200 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). Binary (also known as "Binairo Puzzle", "Takuzu", "Tohu wa Vohu") is played on a rectangular or square grid. The goal is to fill in the grid with digits "0" and "1" according to the following rules: Each box should contain a zero or a one.No more than two similar numbers next to or below each other are allowed.Each row and each column should contain an equal number of zeros and ones (or one more for odd sized grids).Each row is unique, and each column is unique.