As you learn and progress in Sudoku, it will be more challenging and difficult to solve every 9×9 grid. It will require you to think more elaborately, and you might need to explore more sophisticated methods to crack each one. If you need help, here’s a short free guide that can help you become more efficient in deducing numbers.

## Elimination Technique

The elimination technique is a great strategy for both Sudoku beginners and experts. To do this, you simply just have to eliminate the numbers that you can already see on the grids. Like in the first image, you can see that the number 1 is already placed in the C8 box.

This situation also implies that the same number can be placed in either E7 or E9. In this case, placing the number 1 in rows 8, 7, or 9 eliminates the possibility of having the same number in column E. Therefore, the most probable box where you can place 1 is in D2.

### Searching Missing Numbers by Elimination

This method is quite useful once you have almost completed the puzzle. For this example, let’s use row 6. You can see that only two boxes remain empty. 1, 2, 3, 4, 5, 8, and 9 are already in use, so only 2 numbers can be used—6 and 7. Number 6 cannot be placed in H6 because the same number already exists in that column. Therefore, this leaves us with number 7 for H6 and number 6 for B6.

## Pencil Marking Technique

As the level gets more difficult, you will need more elaborate methods to crack the puzzle. The Sudoku Pencil Marking is a conventional technique used by many Sudoku experts, and you may try this too.

Pencil Marking is a systematic process where players write numbers that can be possibly used in a certain box. Numbers are written in small fonts in the corner of each box. This allows players to denote numbers and deduce which ones are supposed to be placed in the empty ones.

To eliminate existing numbers in columns and rows, you can start by looking at column C7 and C8 where the only possible numbers that can be used are 4 and 9. To determine which is to be placed where you must analyze the other grids. Now let’s take a look at A6, this box is already occupied by number 6. Therefore, it cannot be used in column A anymore, so that leaves us with B9.

In cases where the same pair of numbers (4 and 9) can only fit in either of two certain boxes, it is called Disjoint Subsets. If these subsets are very obvious to see, they are called Naked Pairs. In this case, the numbers 4 and 9 are naked pairs. The pencil markings of naked pairs can act as placeholders for these boxes as you try to analyze other grids.