Naked Pair
A naked pair is two cells in the same row, column or box that can only hold the same two digits. Neither digit can go anywhere else in that house.
Ninesmith Sudoku ·
In short
- Find two cells in one house with exactly the same two candidates, say 4 and 8.
- One takes 4 and the other 8; you don't need to know which.
- Strike 4 and 8 from every other cell of that house.
An example
A pair places nothing by itself. It clears candidates, and the clearing often leaves a single behind, as it does here. This board is the start of the puzzle on the home page.
How to spot one
- Write your notes first. Pairs live in the candidates.
- Look for cells with exactly two candidates, then for a second cell with the same two in the same row, column or box.
- Check all three houses: two cells in the same box and the same row give a pair in both.
Naked triples
The same idea works with three cells: if three cells in a house share only three candidates between them, those three digits come out of the rest of the house. The cells don't each need all three. Cells holding 1 and 2, 2 and 3, and 1 and 3 still make a triple.
The reverse is the hidden pair: two digits that fit in only the same two cells.
Common mistakes
- Two cells in different houses. The pair only clears the house both cells share.
- A third candidate. A cell with 4, 8 and 9 is not part of a 4-8 pair.
- Stale notes. A candidate you forgot to strike makes false pairs.
Questions
What is a naked pair in Sudoku?
Two cells in the same row, column or box whose only candidates are the same two digits. Those digits can be struck from the other cells of that house.
Does a naked pair place a digit?
No. It removes candidates. The cells it clears often become singles.
Next: Hidden Pair · Locked Candidates · all techniques
Drill pairs in the Pattern Trainer
Ninesmith Sudoku is a calm Sudoku app for iPhone. Its Pattern Trainer drills naked pairs and triples in sessions of 30 to 90 seconds, and in your own puzzles the Smith names the technique and shows where to look.
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