Box Brain Sudoku
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Easy · technique 8 of 18
Sandwich Sums
A sandwich sum limits where the 1 and the 9 can go.
A Sandwich sudoku technique.
How it works
Try each place the 1 and 9 could sit. Only gaps whose cells can add up to the sum survive, and digits that fit none of them go.
A worked example
Sandwich: in row 6, the digits between the 1 and the 9 add up to 26, so the cell in row 6, column 1 cannot be 2 or 5.
- The area to look at
- The cells that make the pattern
- Candidates it rules out
A real position from a puzzle in the app. Small digits are the candidates the step looks at; coloured digits are already solved.
Practise it in Box Brain Sudoku
The app teaches Sandwich Sums on this same board, then hands you puzzles that need it. When you are stuck mid-game, a hint first points you to the right area, then names the technique and shows the move.