Killer Sudoku strategy
Killer Sudoku adds cage sums to Sudoku. Learn the combinations, the Rule of 45, and how to open a fresh grid.
It is Sudoku plus arithmetic
All the normal Sudoku rules apply, and each dotted cage must add to its printed total with no repeated digit inside. With no given digits, the cage sums are your only way in.
Memorise the unique cage sums
Some totals allow just one combination. Two cells summing to 3 are {1,2}; to 4 are {1,3}; to 16 are {7,9}; to 17 are {8,9}. Three cells to 6 are {1,2,3}. These locked cages crack a grid open.
Use the Rule of 45
Every row, column, and box totals 45. Add the cages that sit inside a unit; whatever is left to reach 45 must live in the one cell that spills in or out. This innie/outie trick is the heart of Killer solving.
Then solve it like Sudoku
Once the cages give you a few digits, ordinary scanning and pencil-mark techniques finish the job.