Variant Sudoku

Killer Sudoku Rules Explained in One Short Example

0:15 · Killer cages · Variant Sudoku

A three-cell cage with a total of 6 shows how killer sudoku works. 2 + 2 + 2 adds up to 6 but repeats a digit, so the cage must hold 1, 2 and 3.

Full lesson and practicePlay Killer Sudoku

Transcript

  1. 0:02The small number is the cage total. These three digits add up to 6.
  2. 0:062 + 2 + 2 is 6, but digits can’t repeat inside a cage.
  3. 0:091 + 3 + 2 = 6 with no repeats. Here the cage must hold 1, 2 and 3.

The rule

In killer sudoku, dashed outlines called cages group cells together. The small number in a cage's corner is the total of its digits, and no digit can repeat inside a cage. Normal sudoku rules still apply to every row, column and box.

Many killer puzzles start with few or no given digits, so the sums do the work. You solve by knowing which digit sets make each total and by adding up whole rows and boxes.

Worth memorizing

  1. Some cages have only one combination.

    Two cells: 3 is 1+2, 4 is 1+3, 16 is 7+9, 17 is 8+9. Three cells: 6 is 1+2+3, 24 is 7+8+9.

  2. No repeats means no 5+5.

    A two-cell cage of 10 can’t hold a 5.

  3. Every full row, column and box adds up to 45.

    Solvers call this the 45 rule, and it cracks most killers.

Practice killer cages in the lesson

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