Naked Pair

Level 3 · Yellow Belt

Strategy:

Requires:

Learn after:

Almost Locked Sets BUG+1 Naked Triple Unique Rectangle Type 1 W-Wing XY-Wing

Overview

A Naked Pair consists of two cells in the same house that contain exactly the same two candidates and nothing else. Since those two digits must occupy those two cells, they can be eliminated from all other cells in the house.

How It Works

Find two cells in the same house that contain exactly the same two candidates.
These two cells will contain those two digits (though we don't know which goes where).
Eliminate both candidates from all other cells in that house.

Example

Starting position

Look for Naked Pair.

Sudoku grid showing the initial puzzle state for Look for Naked Pair.

1

Scan column 1 for a 4 and 5 pair

Find two cells in column 1 that both have only candidates 4 and 5.

Sudoku grid illustrating step 1: Scan column 1 for a 4 and 5 pair — Find two cells in column 1 that both have only candidates 4 and 5.

2

1 was already removed from r1c1

Digit 1 is not a current candidate in r1c1 because earlier solving steps already removed it.

Sudoku grid illustrating step 2: 1 was already removed from r1c1 — Digit 1 is not a current candidate in r1c1 because earlier solving steps already removed it.

3

2 is blocked from r1c1 by row and column

Digit 2 cannot go in r1c1 because r1c6 is in this row and r3c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 3: 2 is blocked from r1c1 by row and column — Digit 2 cannot go in r1c1 because r1c6 is in this row and r3c1 is in this column. Remove the entry or choose a different digit.

4

3 is blocked from r1c1 by row and column

Digit 3 cannot go in r1c1 because r1c9 is in this row and r2c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 4: 3 is blocked from r1c1 by row and column — Digit 3 cannot go in r1c1 because r1c9 is in this row and r2c1 is in this column. Remove the entry or choose a different digit.

5

6 is blocked from r1c1 by the box

Digit 6 cannot go in r1c1 because r2c2 is already in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 5: 6 is blocked from r1c1 by the box — Digit 6 cannot go in r1c1 because r2c2 is already in this box. Remove the entry or choose a different digit.

6

7 is blocked from r1c1 by row and column

Digit 7 cannot go in r1c1 because r1c3 is in this row and r7c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 6: 7 is blocked from r1c1 by row and column — Digit 7 cannot go in r1c1 because r1c3 is in this row and r7c1 is in this column. Remove the entry or choose a different digit.

7

8 is blocked from r1c1 by row and column

Digit 8 cannot go in r1c1 because r1c2 is in this row and r9c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 7: 8 is blocked from r1c1 by row and column — Digit 8 cannot go in r1c1 because r1c2 is in this row and r9c1 is in this column. Remove the entry or choose a different digit.

8

9 is blocked from r1c1 by row, column and box

Digit 9 cannot go in r1c1 because r1c7 is in this row, r4c1 is in this column, and r3c3 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 8: 9 is blocked from r1c1 by row, column and box — Digit 9 cannot go in r1c1 because r1c7 is in this row, r4c1 is in this column, and r3c3 is in this box. Remove the entry or choose a different digit.

9

1 is blocked from r8c1 by the row

Digit 1 cannot go in r8c1 because r8c5 is already in this row. Remove the entry or choose a different digit.

Sudoku grid illustrating step 9: 1 is blocked from r8c1 by the row — Digit 1 cannot go in r8c1 because r8c5 is already in this row. Remove the entry or choose a different digit.

10

2 is blocked from r8c1 by the column

Digit 2 cannot go in r8c1 because r3c1 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 10: 2 is blocked from r8c1 by the column — Digit 2 cannot go in r8c1 because r3c1 is already in this column. Remove the entry or choose a different digit.

11

3 is blocked from r8c1 by the column

Digit 3 cannot go in r8c1 because r2c1 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 11: 3 is blocked from r8c1 by the column — Digit 3 cannot go in r8c1 because r2c1 is already in this column. Remove the entry or choose a different digit.

12

6 is blocked from r8c1 by row and box

Digit 6 cannot go in r8c1 because r8c8 is in this row and r9c3 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 12: 6 is blocked from r8c1 by row and box — Digit 6 cannot go in r8c1 because r8c8 is in this row and r9c3 is in this box. Remove the entry or choose a different digit.

13

7 is blocked from r8c1 by row and column

Digit 7 cannot go in r8c1 because r8c9 is in this row and r7c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 13: 7 is blocked from r8c1 by row and column — Digit 7 cannot go in r8c1 because r8c9 is in this row and r7c1 is in this column. Remove the entry or choose a different digit.

14

8 is blocked from r8c1 by the column

Digit 8 cannot go in r8c1 because r9c1 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 14: 8 is blocked from r8c1 by the column — Digit 8 cannot go in r8c1 because r9c1 is already in this column. Remove the entry or choose a different digit.

15

9 is blocked from r8c1 by row and column

Digit 9 cannot go in r8c1 because r8c2 is in this row and r4c1 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 15: 9 is blocked from r8c1 by row and column — Digit 9 cannot go in r8c1 because r8c2 is in this row and r4c1 is in this column. Remove the entry or choose a different digit.

16

Naked Pair at rows 1 and 8

These cells at rows 1 and 8 form a Naked Pair. The two digits must be split between them.

Sudoku grid illustrating step 16: Naked Pair at rows 1 and 8 — These cells at rows 1 and 8 form a Naked Pair. The two digits must be split between them.

17

The pair claims 4 and 5 for the column

Those two cells must contain 4 and 5, so no other cell in the column can keep those candidates.

Sudoku grid illustrating step 17: The pair claims 4 and 5 for the column — Those two cells must contain 4 and 5, so no other cell in the column can keep those candidates.

18

Removal targets in column 1

Other cells in column 1 still contain 4 and 5 and are removal targets.

Sudoku grid illustrating step 18: Removal targets in column 1 — Other cells in column 1 still contain 4 and 5 and are removal targets.

19

Remove 4 and 5 from column 1

Remove 4 and 5 from the other cells in column 1.

Sudoku grid illustrating step 19: Remove 4 and 5 from column 1 — Remove 4 and 5 from the other cells in column 1.

20

Result

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Naked Pairs are easier to spot than Hidden Pairs because the cells have exactly two candidates.
Look for cells with only 2 candidates and check if another cell matches.
Naked Pairs often lead to chain reactions of eliminations.