How to Fill in Possible Numbers in Sudoku

Solving difficult numbers in sudoku is a process of elimination. By figuring out which numbers cannot fill a square, you narrow your options. Memorizing this method will help you fill in difficult numbers. Eventually, you'll begin see the puzzle just as you see words rather than individual letters.

Instructions

Difficulty: Easy

Things You’ll Need:

• Pencil
• Eraser
• Sudoku puzzle

1. Fill in every blank square with all nine numbers. It doesn't matter if you start at the top like a telephone keypad or at the bottom like ten key, as long as you're consistent throughout.
2. Select a pre-printed number to begin working. Erase that number from the squares you've filled in throughout that column. Put a line across the top of the pre-printed number so you know you've worked the column.
3. Work the same pre-printed number down your row. Erase it from the squares you've filled in, then place a line beside the pre-printed number so you know the row has been worked.
4. Concentrate on the nine-square grid where this pre-printed number resides. Erase that number from all the squares in that grid. Circle the number so you know it's been fully worked.
5. Continue by choosing another pre-printed number. Work all the pre-printed numbers in the same way, following Steps 1 through 4. This is the most methodical way to work through difficult numbers.
6. Review the squares you filled in with possible numbers. Many of them will only have one number left. Choose one to fill in and work that number as you did the pre-printed numbers. Make the same marks so you know what's been worked.
7. Examine the grids to determine where to place any remaining numbers. Even if you have more than one number left for the square, that number will likely only fit into one spot on the nine-square grid.