# Twin Corresponding Sudoku

##### Age 11 to 18 Challenge Level:

##### By Henry Kwok

#### Twin A

#### Twin B

### Rules of Twin Corresponding Sudoku

As with all the Sudoku puzzles published here, the object is
to fill in the whole of each 9x9 grid with numbers 1 through 9 (one
number per cell) so that each horizontal line, each vertical line,
and each of the nine 3x3 squares (outlined with the bold lines)
contain all the nine different numbers 1 through 9.

This problem is different because it consists of a pair of
linked standard Sudoku puzzles each with some starting digits. To
get a complete solution for the twin puzzles, we have to solve each
twin puzzle with the usual strategies but we can only get the
complete solution for the twin puzzles by substituting the
equivalent values of the digits from one twin Sudoku into the
other. So, for example, we can see that in (2,1), that is row 2
column 1, twin A contains the number 4 and twin B contains the
number 7. This means that everywhere a 4 appears in twin A - a 7
appears in twin B and vice versa. This immediately gives you some
more starting digits in each twin!