10 Sudoku techniques > 3. Finding the two missing values

This Sudoku technique is linked to the previous one. When there are only two empty cells remaining in a row, column or region, go through all the possible numbers from 1 to 9 to find out which ones are missing.

If you look at the Sudoku puzzle opposite (puzzle 1), you will see that in row 5, there are only two cells left to complete. If you go through all the numbers from 1 to 9 in your head, you will soon see that the numbers 5 and 7 are missing. As there is already a 7 in column 5, row 3, this value cannot be placed in column 5, row 5. The 7, therefore, has to be placed in column 4, line 5. By a process of elimination, you now know that the last empty cell (column 5, line 5) is going to be a 5.

By the same logic, you can use the numbers in the same regions as the missing values. Take, for example, Sudoku puzzle 2, opposite.

In Column1, there are only two remaining empty cells. Looking at the other numbers in the column, it soon becomes apparent that the missing values are 8 and 9. As there is already an 8 in the lower left region, the missing 8 can only be placed in row 2, column 1. By a process of deduction, the missing 9 has to go, therefore, in the remaining empty cell, row 7, column 1.

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