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## 'Addition Equation Sudoku' printed from http://nrich.maths.org/

#### By Henry Kwok

### Rules of Addition Equation Sudoku

Like the standard sudoku, this sudoku has the basic
rule:

- Every row, every column and every 3x3 box in the grids contains
the digits 1 through 9.

The puzzle can be solved by finding the values of the unknown
digits (all indicated by asterisks) in the squares of the 9x9 grid.
At the bottom and right side of the 9x9 grid are numbers, each of
which is the sum of a column or row of unknown digits marked by
asterisks.

In this puzzle, a set of 17 equations can be formed from the
columns and rows of unknown digits and constants. For example, in
the fourth and fifth columns beginning from the left of the 9x9
grid, the following equations can be formed:

$* + * + * = 6$ and

$* + * = 9$.

In the eighth and ninth rows beginning from the top of the 9x9
grid, the following equations can be formed:

$* + * + * = 11$ and

$* + * = 13$.

After solving all the equations, the puzzle is solved by the
usual sudoku technique and strategy.