Obvious Pairs
Find two cells that can only contain the same two numbers, then eliminate those numbers from other cells in the group.
What Are Obvious Pairs?
The Obvious Pairs technique, also known as "Naked Pairs," occurs when two cells in the same row, column, or 3x3 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.
Key Point
When you find two cells that both contain only candidates {A, B}, you know one cell will be A and the other will be B. This means no other cell in that group can contain A or B.
How It Works
The Process
- 1 Look for cells with exactly two candidates
- 2 Find another cell in the same group with the same two candidates
- 3 These form an Obvious Pair
- 4 Eliminate both numbers from all other cells in the group
Why It Works
If two cells can only contain {2, 7}, then:
- • Either Cell A = 2 and Cell B = 7
- • Or Cell A = 7 and Cell B = 2
- • Either way, 2 and 7 are "used up"
No other cell in that row/column/box can contain these numbers!
Example Walkthrough
Identifying the Pair
Look at this row where two cells (highlighted) both contain only candidates 2 and 7:
Both highlighted cells can only be 2 or 7 - they form an Obvious Pair!
Applying the Eliminations
If other cells in the same row had 2 or 7 as candidates, we could eliminate them:
Before
Other cell candidates: {1, 2, 4, 7, 9}
After
Other cell candidates: {1, 4, 9}
2 and 7 eliminated!
Result
By finding the Obvious Pair {2, 7}, we simplified other cells in the row. This might reveal new singles or other patterns!
When to Use Obvious Pairs
Best Scenarios
- ✓ When singles techniques stop making progress
- ✓ In groups with many bi-value cells (cells with 2 candidates)
- ✓ After filling pencil marks for candidates
- ✓ Medium difficulty puzzles and above
Common Mistakes
- ✗ Confusing with cells that have other candidates
- ✗ Forgetting to check all groups (row AND column AND box)
- ✗ Eliminating from the pair cells themselves
- ✗ Missing pairs in the same box but different rows/columns
Practice Tips
How to Spot Pairs
- 1 Fill in all pencil marks first
- 2 Scan for cells with exactly two candidates
- 3 Look for matching pairs in the same group
- 4 Apply eliminations and continue solving
Related Techniques
- Hidden Pairs - When pairs are hidden among other candidates
- Pointing Pairs - Pairs that point to eliminations elsewhere
- Obvious Singles - The prerequisite technique
Ready to Practice Obvious Pairs?
Look for bi-value cells that share the same two candidates in your next puzzle!
Practice Now