Skip to content
Arctic Sudoku
← All techniques

MediumKiller

Rule of 45 (several cells)

What it is

The 45 rule also gives the total of two to four cells left outside the cages.

How to spot it

When the cages inside a box, row or column cover all but a few cells, 45 minus their total is the sum of the cells that are left. Combine that sum with cage combinations.

Example

1231234510171512
  • Basis
  • Removed / placed
The three cages inside box 1 add up to 5 + 10 + 17 = 32, so r1c3 + r3c3 = 45 − 32 = 13.

Used from level: Hard (Killer Sudoku)