Hidden Pairs
Learn hidden pairs: when two digits can only go in the same two cells of a unit, strip every other candidate from those cells.
A hidden pair is the mirror of a naked pair. Here, two digits can each only go in the same two cells of a unit, but those cells may also show several other candidates, hiding the pair.
Because those two digits are locked to those two cells, every other candidate in the pair can be deleted, leaving a clean naked pair behind.
Hidden pairs are trickier to spot because you scan by digit, not by cell. In the worked example, two cells are the only possible homes for two digits, and everything else in them can go.
Practise the Hidden pair
The best way to learn a technique is to use it. Play a puzzle at the level where it first appears, or drop a tricky board into the solver to watch it in action.
Frequently asked questions
How do I spot a hidden pair?
Look for two digits in a unit that each appear as candidates in only the same two cells. Those cells form the hidden pair.
What do I do once I find one?
Remove every other candidate from the two cells, converting the hidden pair into a naked pair.
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