Naked Pair Walkthrough
A Naked Pair is two cells in the same unit that hold the same two candidates and nothing else. Those two digits are locked into those cells, so they can be removed from every other cell in the unit.
There is a Naked Pair in Row 8. Applying the Naked Pair eliminates 2 candidates (struck out in red below; any solved cells shown in green).
Reading this board
The pattern on this puzzle involves row 8. Work from the before-image above: find the naked pair for yourself before scrolling to the after-image, since the point of a worked example is the search, not the answer. No cell is solved outright by this move. The value is positional: 2 impossible candidates leave the grid, which is what makes the next round of scanning productive.
Why the deduction is valid
When two cells in the same unit show only the same two candidates, those two digits have to occupy those two cells in one order or the other. You do not know which arrangement is correct and you do not need to: either way, both digits are used up inside that pair. Every other cell in the unit is therefore barred from both, even though nothing has actually been solved yet. This is the first technique that produces eliminations without producing a placement, which is why it feels different from singles.
How to spot a Naked Pair on your own board
- Scan for cells holding exactly two pencil marks, then check whether any other cell in the same row, column or box shows that identical pair.
- The two candidates must match exactly. {2,7} and {2,7} is a Naked Pair; {2,7} and {2,7,9} is not.
- Work unit by unit rather than roaming the grid. Take one row, list its two-candidate cells, compare them, then move to the next row.
Common mistakes
- Eliminating inside the pair itself. The two digits stay in those two cells — you strip them from the other cells of the unit, never from the pair.
- Missing the second unit. If both cells of the pair happen to share a box as well as a row, the eliminations apply along both, and solvers routinely take only the obvious one.
What to do next
Naked Pairs rarely solve a cell directly. Their value is that the eliminations often reduce some third cell to a single candidate, so immediately re-scan the unit you just cleaned for Naked and Hidden Singles.