Hidden Pair

Difficulty level: hard

A hidden pair is the mirror image of a naked pair. Two numbers are each restricted to the same two cells of a row, column, or box — but those cells also show other pencil marks, which is what keeps the pair hidden.

Since the two numbers have nowhere else to go, the two cells must hold exactly those numbers in some order. Every other candidate written in those two cells is noise and can be erased.

Hidden pairs are easiest to spot by counting: for each number missing from a unit, note which cells could take it. Two numbers sharing the same two-cell list form the pair.

Worked example

In the top band, 2 and 7 are blocked everywhere except the two highlighted cells — they form a hidden pair, so any other pencil marks there can be erased.
(highlighted)
(highlighted)
2
7
2
7

How to apply it

  1. Pick a unit and list, for each missing number, the cells that can take it.
  2. Find two numbers whose candidate cells are the same two cells.
  3. Erase all other pencil marks from those two cells.
  4. The cleaned-up cells often turn into naked singles or pairs — re-scan.

Practice it

The fastest way to internalize the hidden pair is to use it. Play a free hard puzzle — the in-game hint system points out exactly this pattern when it appears, or browse the full technique library.