The fourth installment of the successful Times Killer Su Doku series. Adding the challenge of arithmetic and taking Su Doku to a new deadly level of difficulty.

The puzzles use the same 9x9 grid as normal Su Doku but with an added mathmatical challenge. The aim is not only to complete every row, column and cube so that it contains the digits 1-9, it is also necessary to ensure that the outlined cubes add up to the same number.

With 150 new Killer Su Doku puzzles, you can ease yourself in with the Moderate before taking the plunge and tackling the real killers:

• 20 Moderate
• 50 Tricky
• 50 Tough
• 30 Deadly

For those who like to live dangerously and push beyond their mental comfort zone, steel yourself for The Times' toughest collection yet.