Solving techniques
Hidden pair
A hidden pair is the mirror image of a naked pair. You find two digits, not two cells, and you clear the other candidates out of the cells.
A hidden pair is two digits that appear as candidates in only two cells of a row, column or box. Those two digits must go in those two cells, so every other candidate can be removed from both cells.
The logic
If digits A and B can only go in cells X and Y of a unit, then X and Y must hold A and B. Any other candidate listed in X or Y is impossible and can be erased.
How to find a hidden pair
- Choose a unit and write notes.
- For each digit, count how many cells in the unit still list it.
- Find two digits that appear in exactly the same two cells.
- Remove all other candidates from those two cells.
Naked pair or hidden pair?
In a naked pair, the two cells show only two candidates, so it is easy to see. In a hidden pair, the cells show extra candidates that hide the pattern, so you must count digits. A hidden pair is often easier to find once you have noticed the digits.
Common mistakes
- Counting a digit that has already been placed in the unit.
- Removing candidates from cells outside the pair.
- Not checking that both digits appear in both cells. If one appears in only one of them, it is a hidden single instead. See hidden single.
Frequently asked questions
What is a hidden pair?
Two digits that can only go in the same two cells of a unit.
What do you remove?
All other candidates from those two cells.
Why is it called hidden?
Because the cells also list other candidates that hide the pair.