These diabolically difficult Ultimate Killer Su Doku puzzles will really put your brain power to the test as you "warm up" with the 150 Deadly Killer puzzles before steeling yourself to take on the 50 Extra Deadly Su Dokus. The puzzles use the same 9x9 grid as a regular Su Doku, but have an extra mathematical element. The aim is not only to complete every row, column, and cube so that it contains the digits 1 to 9, but also to make sure that the outlined sections, called cages, add up to the number given in each cage.