The Times Ultimate Killer Sudoku Book 10 by HarperCollins Distribution Services

Specially compiled to provide the most deadly Su Doku challenge, this is the only volume for Su Doku enthusiasts who need
a puzzle that really tests their mettle.

Prepare yourself for the toughest Su Doku challenge there is. These diabolically difficult Ultimate Killer
Su Doku puzzles will really put your brainpower 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. Are you ready for the challenge?

Not for the faint-hearted. The puzzles use the same 9×9 grid as a regular Su Doku but have an extra mathematical element that multiplies the challenge. 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.