Peak Sudoku

Hidden Pair

Two digits in a house that can only go in the same two cells, clearing all other candidates from those cells.
All techniques

Overview

Tier 3
Subsets
Typical difficulty
Peak Score 35–50
Also known as
Concealed Pair, Hidden Twin

When two digits appear as candidates in only two cells within a house, those two cells must contain those two digits. All other candidates in those two cells can be eliminated.

A Hidden Pair is the subset counterpart to a Hidden Single. While a Naked Pair eliminates digits from the *rest of the house*, a Hidden Pair eliminates other candidates from *inside the pair's own cells*. They are termed 'hidden' because the two cells may contain extra candidate digits that camouflage the pair until you scan the house digit by digit.

Worked examples

1 / 5
Reading the exampleCells losing candidatesEliminated candidates
In row 5, the digits 3 and 8 can only go in R5C2 and R5C3. Those two cells must take those two digits, so every other candidate can be removed from them.
Removes: 7 from R5C2, R5C3 · 5 from R5C2 · 1 from R5C2, R5C3 · 4 from R5C2, R5C3 · 2 from R5C2, R5C3

How to apply it

Spotting the pattern and making the deduction, in order.

  1. Scan a row, column, or 3×3 box digit by digit rather than cell by cell.
  2. Identify two digits that only appear as candidates in the exact same two cells of that unit.
  3. Because the unit needs both numbers, one must land in the first cell and the other in the second cell.
  4. Neither of those two cells can ever hold any other value.
  5. Clear all other candidate pencil marks from those two cells, leaving behind a clean pair.

Common mistakes

  • Leaving extraneous candidates in the two cells after identifying the pair.
  • Missing the pair because one of the cells has four or five candidates written in it.
  • Forgetting that both digits must appear in *both* cells and *nowhere else* in that house.

Frequently asked questions

How is a Hidden Pair different from a Naked Pair?
In a Naked Pair, the cells contain *only* those two digits ({2, 7} and {2, 7}). In a Hidden Pair, the cells contain other numbers too ({2, 5, 7} and {2, 7, 9}), but 2 and 7 appear nowhere else in the house.
What do I eliminate when I find a Hidden Pair?
You eliminate all *other* candidates from those two specific cells. You do not eliminate from other cells in the house.
Peak Score 30–45Naked PairTwo cells in the same house contain exactly the same two candidates.Peak Score 45–60Hidden TripleThree digits confined to the same three cells of a house, clearing all other candidates from those cells.

Put Hidden Pair into practice

Try a puzzle from the Medium tier (Peak Score 31–40).

Play a Medium puzzleAll 25 techniques