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Killer sudoku for beginners

You already know enough sudoku if you know that each row, column, and 3×3 box contains the digits 1 to 9 once. Killer adds cages. A cage is the dashed outline. The tiny number is the sum of the digits inside it. Those digits do not repeat, even when the cage is only two cells. On harder puzzles there are no given digits at all. The sums are the clues.

Memorize eight combinations and you can start today. 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, 7 is 1+2+4, 23 is 6+8+9, 24 is 7+8+9. When you see one of those cages, pencil the digits in. You will place them as soon as one of them is blocked by the row or the box.

The other beginner move is the 45 rule. Each row adds up to 45 because 1+2+…+9 = 45. If you can add up every cage that sits entirely in a row, the cell left over is 45 minus that total. It feels like a magic trick the first time and like ordinary bookkeeping the second.

Use notes. On this site, Notes is a button and the N key. Write only the digits the cage still allows. When a cell has one digit left, it is done. When a digit has one cell left in a row, it is done. Those two sentences are the whole of “singles,” and every puzzle you should be playing as a beginner is solved by them plus the combinations above.

Do not guess. If you cannot name the reason a digit goes in a cell, leave it. Guessing produces two digits that both seem to finish a cage and then a contradiction ten minutes later. The puzzles here are checked so that a reason exists. The hint button will say what it is, and it will not type the digit unless you ask again.

Play today’s easy puzzle, then the combinations page with “2 cells” selected, and print it if you like paper. When unique cages feel slow rather than clever, move to medium. That is the entire on-ramp.

Play a medium puzzle or open the combination sheet.