This is a simple way to solve Sudoku that's great for beginners. The technique is named for what it does: you find the missing number in the block. To do this, we look:
- which values are already in the central 3x3 block: 2, 4, 6, 3 and 7;
- which numbers are missing in the block: 1, 5, 8 and 9;
- which numbers are in the row (3, 6, 7, 4);
- which numbers are in the column (8, 9, 2, 3, 1).
If we use the method of elimination, we can see that in the intersection cell (marked with an orange frame), the only possible digit is a five. So we just write the number 5 in the cell.
Just a quick check to make sure everything's in order! We can't use numbers 1, 8 or 9 because they're already in the column, and number 5 isn't in the column or row. The Sudoku rule that digits can't be repeated in the same block, vertical or horizontal, is followed.
The "Last Free Cell", "Last Possible Number" and "Last Remaining Cell" methods are some of the most basic ways to solve Sudoku. Once you've got the hang of these, you can move on to the more complicated ones.