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Obvious Pairs Technique

Beginner

The Obvious Pairs technique, also known as "Naked Pairs," occurs when two cells in the same row, column, or 3×3 box can only contain the same two numbers. When this happens, these two numbers are "locked" into those two cells, allowing you to eliminate them from all other cells in that group.

How It Works

When you find two cells in the same group (row, column, or box) that each have exactly the same two candidate numbers, you know that these two numbers must be distributed between these two cells. This means you can eliminate these numbers from all other cells in that group.

Example 1: Obvious Pair in a Row

Look at this row where two cells form an obvious pair:

Before: Identifying the Pair

5
3
2
7
8
1
9
2
7
6
4
8
1
9
3
7
5
6
2
4
1
2
3
4
5
6
7
8
9
6
4
9
1
2
3
4
5
6
7
8
9
3
1
7
8
→

After: Eliminations Applied

5
3
2
7
8
1
9
2
7
6
4
8
1
9
3
7
5
6
2
4
1
2
3
4
5
6
7
8
9
6
4
9
1
2
3
4
5
6
7
8
9
3
1
7
8

1Identify the pair: Cells in positions 3 and 7 of the top row both have candidates 2, 7

2Lock the numbers: Since these are the only two cells that can contain 2 or 7, they must contain these numbers

3Apply eliminations: Remove 2 and 7 from all other cells in the same row

4Result: The other cells in the row can no longer contain 2 or 7, simplifying their candidate lists

Example 2: Obvious Pair in a 3×3 Box

Here's an obvious pair within a 3×3 box:

5
3
7
8
1
9
2
6
4
8
1
9
3
7
5
6
2
4
2
6
4
9
2
3
1
7
8
1
7
2
5
8
4
9
3
6
3
9
6
1
4
7
8
5
2
6
2
8
7
3
1
4
9
5
4
5
1
2
6
9
2
6
3
8
7
7
8
3
4
5
1
2
3
4
5
6
7
8
9
1
1
9
9
4
5
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
8
7
4
3

In this example, the center-bottom 3×3 box contains an obvious pair:

1Pair identification: Positions (7,4) and (7,6) both contain only candidates 2, 6

2Box constraint: Since these are the only cells in the box that can contain 2 or 6, they must contain these numbers

3Eliminations: Remove 2 and 6 from all other cells in the same box (shown with strikethrough)

Step-by-Step Process

  1. 1Look for matching candidates: Find two cells in the same group with identical candidate sets
  2. 2Verify they form a pair: Both cells must have exactly the same two candidates
  3. 3Identify elimination targets: Find all other cells in the same group (row, column, or box)
  4. 4Apply eliminations: Remove the pair numbers from all other cells in that group
  5. 5Check for new singles: See if eliminations created any new obvious singles

Requirements for Obvious Pairs

When to Use This Technique

⚠️ Common Mistakes to Avoid

Advanced Applications

Practice Tips

  1. Use pencil marks: Write candidate numbers in cells to make pairs visible
  2. Systematic approach: Check each group (row/column/box) methodically
  3. Start simple: Look for pairs in groups with fewer empty cells first
  4. Double-check eliminations: Verify you're removing from the correct cells
  5. Look for follow-ups: Check if eliminations create new solving opportunities

Why This Technique Works

The obvious pairs technique works because of the fundamental constraint that each number 1-9 must appear exactly once in every row, column, and 3×3 box. When two cells in a group can only contain the same two numbers, these numbers are effectively "reserved" for those cells, making them unavailable to any other cell in that group.