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Product Sudoku

Age 11 to 14 Challenge Level:

Alison and Charlie kept a record of the order in which they filled the Sudoku.
They filled the cell marked 1 first, then the cell marked 2, then the cell marked 3...
You might like to retrace their route to fill in the cells in the same order, though this is just one possible route through the problem.

You can print their journey here