The case notes
Find two digits confined to two cells
A hidden pair is two digits that have only the same two places in a row, column or box. The cells may still show other pencil marks. Watch a worked example, then try the idea in a puzzle.
Put it into practice
Two digits · two places
A hidden pair is two digits that have only the same two places in a row, column or box. The cells may still show other pencil marks.
Row needs 1, 2, 3, 4, 5
This row has five gaps. It needs one through five. At first, the first two cells could each hold any of them.
Columns 3–5 block 1 and 2
Look below the third, fourth and fifth gaps. Each of those columns already has both a one and a two. Neither digit can go in any of those three gaps.
First two cells reserve {1, 2}
So one and two must occupy the first two cells, in either order. Their extra three, four and five marks cannot be right. Remove them.
Two places for 1 and 2
The digits told us where to look. The pair stays unresolved, but both cells are now cleanly narrowed to one or two.
Read the transcript
A hidden pair is two digits that have only the same two places in a row, column or box. The cells may still show other pencil marks. This row has five gaps. It needs one through five. At first, the first two cells could each hold any of them. Look below the third, fourth and fifth gaps. Each of those columns already has both a one and a two. Neither digit can go in any of those three gaps. So one and two must occupy the first two cells, in either order. Their extra three, four and five marks cannot be right. Remove them. The digits told us where to look. The pair stays unresolved, but both cells are now cleanly narrowed to one or two.
