Technique

Hidden Pair

Two digits that, within a house, only have room to go in the same two cells - even if those cells still list other candidates too. Once spotted, every other candidate can be stripped from just those cells.

💡 What It Is

The flip side of a naked pair: instead of two cells sharing exactly two candidates, two digits share exactly two possible cells.

🔍 How To Spot It

For a house, check where each digit 1-9 could still go. If two digits are each only possible in the same two cells, that's a hidden pair - even if those cells have other candidates listed too.

✅ Why It Works

Those two digits have nowhere else to go in the house but those two cells, so the cells can't hold anything else.

📝 Worked Example

3956

3912

In box 6, digit 3 and digit 9 can each only go in R4C8 or R6C9 (both cells still list other candidates). Since 3 and 9 have to fill those two cells, remove every other candidate from R4C8 and R6C9.

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