- Look at the numbers in the row, column and box of this cell.
- Every number except 8 is already used there.
- So this cell must be 8.
Naked Single in sudoku
A Naked Single is an empty cell that can take only one number: the other eight already stand in its row, its column or its box. With notes filled in, it is a cell with one note left.
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How to spot it
Pick an empty cell and collect the numbers in its row, column and box. If eight different numbers show up, the ninth goes in the cell. Cells where a crowded row meets a crowded column are the likeliest. Notes make these cells obvious: one small number in a cell is a Naked Single.
Why it works
A cell may not repeat a number from its row, column or box. If those three hold every number but one, that one is the only number the cell can take.
On a real puzzle
This is Naked Single on its practice puzzle, at the first step that needs it. The game's hint explains the step like this:
Practice it
This Easy puzzle is solved with singles alone, from the first number to the last. If you get stuck, the hint shows the next one and names it.