From Sudopedia, the free Sudoku reference guide

From Sudopedia

In Killer Sudoku, the player is presented with a number of cages that are shown explicitly. The player may find additional cages, via the application of the 45 rule. Such cages are called hidden cages.

Example

Consider the following example.

This row has two outies (i.e., the two cells jutting out at the bottom), and the cage sums add up to 12 + 19 + 19 + 4 = 54. Since the cells in the row must add up to 45, the sum of the outies must be 54 - 45 = 9.

Hence, we have a hidden cage 9[2], as indicated in the diagram above.

Note

If the cells in a hidden cage does not belong to the same house, then the Killer Convention does not apply to this hidden cage. In other words, such cells can contain the same digit so long these cells add up to the required cage sum.

See Also

• 45 rule
• Split cage