LeafyOrb

Sudoku techniques · Medium level

Naked pairs: two cells, two digits

A naked pair is two cells in the same row, column or box that can each hold only the same two digits. Those two digits are used up by the pair, so you can remove them from every other cell in that row, column or box.

How it works

Say two cells in a row both allow only 5 and 6. You do not know which is which yet, but one will be 5 and the other 6. That means no other cell in the row can be 5 or 6.

A naked pair does not place a digit. It clears candidates, and that often leaves a single somewhere else. You need pencil marks to see it. If the two cells share a box and a row or column, the pair clears both.

  • The row, column or box the move uses
  • The cells that make the pattern
  • Candidates the move removes
Naked pair example on a Sudoku board: R1C2 and R1C3 can only hold 5 and 6 between them, so in box 1 no other cell can use those digits.

Example 1 · Box · from Medium puzzle #32

R1C2 and R1C3 in box 1 can only be 5 or 6. One of them takes the 5 and the other the 6, so no other cell in box 1 can. Remove 5 and 6 from R3C2 and R3C3.

Play this position in Ninebloom: Home › Your own puzzle, then paste the code. NG-1ARPNS-1BXLIA-DFJ3SP-5ST6ZS-4MXI5E-AI9ZBJ-AKFLG5-3V3BI6-XJA3H

Cells are named by row and column: R4C3 is row 4, column 3. Boxes are numbered 1 to 9, left to right and top to bottom.

How to spot it

  1. Fill in pencil marks for the row, column or box you are looking at.
  2. Look for cells with exactly two candidates.
  3. Find two of them with the same two digits in one row, column or box.
  4. Remove those two digits from every other cell in the shared row, column or box.

More examples

Naked pair example on a Sudoku board: R2C7 and R2C9 can only hold 8 and 9 between them, so in row 2 no other cell can use those digits.

Example 2 · Row · from Medium puzzle #47

R2C7 and R2C9 in row 2 can only be 8 or 9. One of them takes the 8 and the other the 9, so no other cell in row 2 can. Remove 8 and 9 from R2C4.

Play this position in Ninebloom: Home › Your own puzzle, then paste the code. NG-1GQ03Q-IJBQQM-265TPJ-SXAC8Z-Q4WJ7X-7CKYY7-D9GGR4-5PXGDT-BD8G0
Naked pair example on a Sudoku board: R8C8 and R9C8 can only hold 1 and 9 between them, so in column 8 no other cell can use those digits.

Example 3 · Column · from Medium puzzle #72

R8C8 and R9C8 in column 8 can only be 1 or 9. One of them takes the 1 and the other the 9, so no other cell in column 8 can. Remove 9 from R4C8 and R6C8.

Play this position in Ninebloom: Home › Your own puzzle, then paste the code. NG-24QO30-O9T8PT-2STJKH-AB7B9F-201XSS-W7AI4K-935CWZ-JLO898-9CIMR

Common mistakes

  • Using a cell with three candidates. Both cells must allow exactly the two digits, nothing else.
  • Removing digits from the wrong place. Clear only the row, column or box the two cells share.
  • Missing a pair because the pencil marks are out of date. Clear old marks as you place digits.

Questions

What is the difference between a naked pair and a hidden pair?

In a naked pair, the two cells hold only the two digits. In a hidden pair, two digits can only go in two cells, but those cells may hold other candidates too. Both say the same thing from different sides.

Is there a naked triple?

Yes. Three cells in a row, column or box that between them hold only three digits work the same way. Each cell does not need all three; together they must use no more than three.

Which Ninebloom level uses naked pairs?

Medium. Medium adds naked pairs and pointing pairs to the singles.