Hidden pair
HardWhen two digits can each go in only the same two cells of a row, a column or a box, those two cells hold those two digits. Every other candidate in those cells can go.
How to spot it
- With notes, look for two digits that appear in only two cells of a unit: the same two cells.
- Those cells belong to the pair.
- Remove every other candidate from them.
Why it works
Each of the two digits must go somewhere in the unit, and they only have two cells between them, so they fill those cells.
Example
7
9
4
6
1
2
9
6
1
4
2
3
5
8
6
9
7
2
5
6
1
6
4
9
1
7
8
5
2
6
3
1
5
6
1
6
7
5
9
6
3
7
8
1
Look at where 4 and 9 can go in row 4.
Common mistakes
- Looking at cells instead of digits: a hidden pair is found by asking where each digit can go.
- Removing the two digits from other cells: they weren’t there to begin with.