Hidden singles: find the digit's only home

A hidden single is about the whole unit, not one cell. A cell can contain several pencil marks and still be forced if one digit appears nowhere else in that row, column, or box.

Try three practice positions

Key idea

Choose one digit and find the only cell in the unit that can still contain it.

See the move, step by step

Scan the top-middle 3×3 box for the only possible home for digit 8.

Step 1 of 3

Choose a unit and a digit

Focus on box 2 and look only for digit 8. Several cells are unsolved, so the answer is hidden among a realistic field of notes.

Unit being scanned

Step 2 of 3

Compare candidate locations

The other open cells in box 2 do not contain candidate 8. R1C6 does, so 8 has only one possible home in the box—even though R1C6 still shows 2, 4, and 6 as cell candidates too.

Other candidate cellsOnly cell containing 8

Step 3 of 3

Place the hidden single

Place 8 at R1C6 and update its peers. The cell did not look solved by itself; scanning the whole box made the placement certain.

Placed 8

Try three practice positions

Make one deduction in each position. All pencil marks come from the displayed grid. These are short technique exercises, not full puzzle completions.

Progress lasts while this lesson is open. Start again to reset these three exercises.

0 of 3 correct

Exercise 1 of 3

Guided

Inspect this unit: row 9. Where must 6 go? Select the cell.

Select a cell, then check your move. Use arrow keys to explore the board. The selected cell’s candidates are also shown below at a larger size.

Select a cell to inspect its candidates.

Try it on today's puzzle

After every naked-single pass, choose one digit and scan it across each row, column, and box. Hidden singles become obvious when you keep the digit fixed.

Play today