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This technique involves choosing a number and locating the possible cells in which it can be placed. By a process of elimination, you can rule out the columns, rows and regions in which the number already appears. We recommend you begin by working out which numbers appear the most frequently in the puzzle and subsequently try and locate the missing values. The more frequently the numbers appear in a game of Sudoku, the easier the missing value is to locate as there are significantly fewer possibilities.
Let’s take a concrete example. In the Sudoku puzzle opposite, there is no 6 in the central region. Use the other 6s in the puzzle to help you to place it. It cannot be in row 4, as there is already a 6 in this row, in the centre right region. Neither can it go in row 5 because there is already a 6 in the centre left region of this row. There is therefore only one possible place left: column 5, row 6. While this solution was found by using horizontal clues, vertical clues also indicate that a 6 in the upper central region would rule out a 6 in column 4. In this case, however, the vertical clues were not key to finding the solution.
Having found the value, check to see if the new number will allow you to place another value, as is the case in the above example. The 6 in the lower central region cannot be placed in columns 4 and 5. Neither can it be placed in row 9. Consequently, there is only one possible place for it: column 6, line 8. We have added the new 6 in red to show you.
Put this technique to the test with one of our online Sudoku puzzles |
