A hidden pair is like a naked pair, but buried among other candidates. Two numbers appear in only two cells within a group. The other candidates in those cells are distractions.
What is a hidden pair?
In a row, column, or box, if two numbers can only go in the same two cells, those cells must contain those numbers. You can erase all other candidates from those two cells.
Only these two cells can hold 4 and 6 in this row. Other candidates in them can be removed.
Naked vs hidden
The difference is what you look at. Both lead to eliminations, just from opposite directions.
Naked pair
Two cells show only two candidates. Remove those from other cells.
Hidden pair
Two candidates appear in only two cells. Remove other candidates from those cells.
How to find them
Pick a row, column, or box. For each number not yet placed, count how many cells can hold it. If two numbers both appear in exactly the same two cells, you found a hidden pair.
- Choose a group (row, column, or box).
- For each missing number, list which cells can hold it.
- Find two numbers that share the same two cells. Erase other candidates from those cells.
Numbers 1 and 9 can only go in these two cells. Remove 5 and 8 from them.
Tips
- Hidden pairs are common but easy to miss. Take your time.
- After cleaning up a hidden pair, look for new naked singles.
- Boxes often have more hidden pairs than rows or columns.
Practice
Hidden pairs require patience. The more you look for them, the faster you get at spotting where two numbers are restricted to the same two cells.