Improve Your Mental Focus, Boost Your Brain Powers, and enjoy your time solving the Killer Sudoku puzzles. Sudoku games have been scientifically proven to improve mental focus, Sharpen the memory as well as protecting the brain from neurodegenerative disorders. This Book has 400 Puzzles of killer Sudoku in 4 levels, from Hard to extremely hard (100 Puzzles in each level). Answers to all the puzzles are included at the end of the book. Killer Sudoku cheat sheet for unique sum combinations included What is killer Sudoku, aka Sum Sudoku or sumdoku? And how to solve them? You start with an empty grid and only given the sum of caged cells written in small font on the upper left corner of the cage. You have to work out the summation and find the numbers in the cage, region, row, and columns. Of course, you will use every tip and trick used for traditional Sudoku and more. As any Sudoku puzzles, numbers from 1 to 9 to be placed in a row or column or region with no repetition. There are many tips to solve traditional Sudoku especially elimination and exclusion and logic. But for killer Sudoku the rule of 45 and unique sum are one of the most important clues to solve the puzzle. (More instruction and tips can be found inside the book.) Features: Size: 8 x 11.5 inch (large size) with softcover and paperback binding so easy store and use. Pages: 132 pages with full-page 400 different puzzles. Plus the solutions of all the puzzles at the end. Plus 10+ Bonus puzzles of different Sudoku variant Killer Sudoku cheat sheet for unique sum combinations included. Improve your mental focus with this unique selection of easy, fun killer Sudoku puzzles. Scroll up and order your copy.