This is an example of a completed Sandwich Sudoku puzzle.
The usual rules of Sudoku apply, and the grid contains additional 'Sandwich' clues outside the grid on the right and on the bottom.
These clues tell you the total of the values between the 1 and the 9 in that row or column.
For example, we can look at the sum of the values between the 1 and the 9 for the first three rows,
- 2+8+4+5+7+3 = 29
- 8+3 = 11
- 2+6+8 = 16