A hidden pair occurs when two digits can only be placed in the same two cells within a house, even though those cells have other candidates too.
Understanding the Concept
Two candidates appear in only two cells within a house (row, column, or box).
These two cells might have other candidates, making the pair "hidden" among the extras.
Since these two digits must go in these two cells, all other candidates can be removed from these cells.
After cleanup, it becomes a naked pair.
Example: If digits 3 and 7 only appear in cells A and B within a row, then A and B can only contain 3 or 7.
Hidden pairs are harder to spot than naked pairs because extra candidates camouflage them.
Examples
Hidden Pair {6, 9} in Column 0
In column 0, digits 6 and 9 can only go in R2C0 and R6C0. Both cells have other candidates too, but since 6 and 9 are confined to just these two cells, we can eliminate all other candidates from them.
Pro Tips
- •For each pair of digits, check where they can go in each house
- •If both are limited to the same two cells, you have a hidden pair
- •After finding one, clean up the cells to show only the pair
- •Hidden pairs often become naked pairs after cleanup
