Strategies
Beginner
Hidden Single Technique
Find numbers that can only fit in one specific cell within a unit.
Interactive Practice
Find the number for the highlighted cell
Apply Technique
7
7
?
7
Find the number for the highlighted cell:
Hidden Single Technique
A Hidden Single occurs when a number can only fit in one specific cell within a row, column, or 3x3 block, even though that cell might have multiple other candidates.
Rules:
- Pick a number from 1 to 9 (e.g. 5) and scan a 3x3 block.
- Use the surrounding rows and columns to cross off cells in that block where 5 cannot go.
- If only one cell in the block can possibly hold the 5, place it there immediately.
Hint
- Scan the board number-by-number (all 1s, then all 2s, etc.).
- Hidden singles in 3x3 boxes are usually the easiest to spot.