Lesson 7 · Solve safely
Common Sudoku Mistakes
Recognise guessing, missed conflicts, and unreliable notes before they derail a puzzle.
See the logic move
Use Next to reveal each reason. On the final step, tap the highlighted cell to complete the move yourself.
Step 1 of 3
Focus
row 3, column 7 currently allows 1, 3, 4, 5, 7.
Select an empty cell to see its legal candidates and why the other digits are blocked.
- 1
row 3, column 7 currently allows 1, 3, 4, 5, 7.
- 2
Inspect R3C7 and then check its row, column, and 3x3 box.
What the board is showing
Explain it simply
Mistakes usually happen when we rush. A short three-way check keeps the board trustworthy.
Step by step
- Avoid guessing between two candidates.
- Recheck row, column, and box.
- Keep candidate notes current.
- Pause after each placement.
From demonstration to independent solving
Prove the move yourself
What you should be able to do
Recognise the difference between a legal possibility, a forced deduction and an unsupported guess.
Read the exact board evidence
R3C7 allows 1, 3, 4, 5 and 7 on the example board. Entering 5 may happen to match the final solution, but the candidate list alone does not prove it. The safe move is to continue until a unit-level pattern singles out one option.
When the logic is strong enough
A correct final digit is not automatically a correct logical move. Your reason must follow from the visible board at the moment you place it.
Train the pattern without guessing
When tempted to choose between candidates, write one sentence beginning 'This must be… because…'. If the sentence cannot rule out every alternative, move to another unit.
Quick check: What is the safest action when two candidates remain and neither is proven?
Leave both notes and continue solving elsewhere.
Turn logic into skill