Active Brain Series gigantic book of 1800 extra hard Sudoku puzzles with solutions, perfect for the Sudoku enthusiast. With only one level of difficulty there are no wasted puzzles. Sudoku is a fun way to exercise your brain and there are plenty of puzzles in this book to give it a really good workout! The book is 8.5" by 11" and has 4 puzzles per page with room for notes.