Pointing Pairs

How It Works

When all candidates for a particular number within a 3x3 box are confined to a single row or column, that number can be eliminated from other cells in that row or column outside the box.

Step by Step

1. Within a 3x3 box, find a candidate number that only appears in one row (or column).
2. Since it must go in that row within the box, eliminate it from the same row outside the box.

When to Use

Use Pointing Pairs when a candidate in a 3x3 box appears only in one row or one column within that box. You can then eliminate that candidate from the rest of that row or column outside the box.

Example

In a box, the number 3 appears as a candidate only in the top row of the box. Since 3 must go in that box and only in that row, it cannot appear in the other two cells of that row outside the box.

Common Mistakes

Applying the elimination to the wrong cells. Remember: you eliminate from the same row or column outside the box, not from other cells inside the box.

Tips

Focus on one box at a time. For each candidate number, check if all its positions in the box lie in a single row or column. If yes, you have a pointing pair (or pointing triple).