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Sudoku Strategy

Welcome to the Hints and Tips section of The Puzzle Club. Here we look at strategies you can use to help you solve our Sudoku puzzles.

Using Logic To Deduce The Answer

We have looked at both elimination and cross-referencing so far, and also using pencil marks to help reduce the options available to solve a puzzle. Here we look at how to use logic to deduce what the value of a cell must be. We'll do this again by means of an example:

sudoku grid

Imagine you are trying to work out where the '2' goes in the first 3 x3 box at the top left of the image. Now, we can use the rules of elimination already discussed to eliminate three places; marked with red 'X's on the diagram. And three cells already have values. This leaves just three places: top middle, top right and middle right. But we can do better than this!

To see how, let's try to find the location of the '2' in the second 3 x 3 box, the dark yellow box at the top middle of the diagram. Now, using the elimination technique we know it must go at either the top left or top right of that box. Let's mark it below:

sudoku tips

We can use this knowledge to now place the '2' for sure in the first box! Whilst we don't know exactly where the two goes in the middle box, as just described we know for sure it is in the top row of that box. And hence a '2' cannot also go in the top row of the first box, because then we would break a rule having two '2's in one row. This only leaves one possible place for this '2'; the middle right square, and we place it accordingly:

sudoku puzzle solved

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