The ‘Obvious Pairs’ is also called ‘Naked Pairs’. This method is based on the same principle as the ‘Obvious Singles’ technique. Find all possible candidate numbers in each cell and identify pairs of cells within a 3×3 block having similar two candidate numbers.
For example, in image 1 below, you have now filled all the cells with candidate numbers. Now consider a 3×3 block highlighted with the purple frame. Now you see that the numbers 5 and 8 are recurring in two cells highlighted with the green frame. Since these two cells can only be filled by either of them (5 or 8), this is our ‘Obvious Pairs.’
The next step is to figure out which other cells hold the number 5, and which one contains the number 8 as shown in image 2. As such, you can remove both 5 and 8, thus leaving you with one unique digit in each cell. This process identifies ‘The Obvious Single’ for you to fill in as shown in image 3. Now write down the winner numbers 6, 7, and 9 into their respective cells as shown in image 4, after that you can proceed to solve this puzzle using other techniques.
By mastering the ‘Obvious Pairs’ technique, you can solve more complex puzzles with confidence. To know more about this technique, refer an article from University of Cambridge. Once you have a good grasp of this technique, download our free printable Sudoku puzzle books!