Daily Challenge
Let the Sudoku Box Decide
Two candidates fit a Sudoku cell's row and column. Use its 2x2 box to find the certain number, with an optional hint and complete checked solution.
Difficulty: Easy
Sudoku practice: 2 of 2. Try this round on its own, or warm up with One Certain Sudoku Number.
Two choices are not a reason to guess
Find B1: column B, row 1, marked with a question mark. This small Sudoku uses 1, 2, 3, and 4 once in every row, column, and thick-bordered 2x2 box. Keep the printed clues fixed. Dots are empty cells; the question mark is also empty.
The first row needs 2 and 3. Column B does not yet contain either number. What does the upper-left box tell you?
| Row | A | B | C | D |
|---|---|---|---|---|
| 1 | A1: 1 | B1: target, empty | C1: empty | D1: 4 |
| 2 | A2: 3 | B2: empty | C2: 1 | D2: 2 |
| 3 | A3: empty | B3: 1 | C3: 4 | D3: empty |
| 4 | A4: 4 | B4: empty | C4: empty | D4: 1 |
This is a fixed, read-and-solve exercise, not an interactive game. Find just B1 first, or work out the remaining cells on paper.
Show a small hint
The upper-left box contains A1, B1, A2, and B2. Look at A2. Would one of your two candidates repeat that clue inside the box?
Answer: check the third group
B1 is 2. Row 1 already has 1 and 4, leaving 2 or 3. Column B contains 1 but no 2 or 3, so it does not settle the choice.
The upper-left box contains 3 at A2. Placing 3 at B1 would repeat it in that box. That removes 3 and leaves 2. The same box has no 2, and neither the row nor the column has a 2, so the placement is allowed by all three groups.
Now row 1 is 1, 2, blank, 4. That makes C1 equal to 3. Check column C and the upper-right box before placing it: neither contains a 3. One certain answer opens the next step.
This is different from choosing whichever candidate looks likely. The box rules out one choice with a visible clue.
Show the complete solution
Rows from top to bottom, columns A to D:
- 1, 2, 3, 4
- 3, 4, 1, 2
- 2, 1, 4, 3
- 4, 3, 2, 1
Every starting clue stays unchanged. All rows, columns, and 2x2 boxes contain 1 to 4 exactly once. This board has one solution.
Choose your next break
Read Your First Sudoku Move to revisit the three checks, or try Daily Number Puzzle for a number-order warmup. That playable starter asks you to tap numbers in order; it is not Sudoku.
For a full-size puzzle, play DaySudoku, a related external daily Sudoku site with a Key9 twist. Find the Key9 first, then continue the full Sudoku. This teaching board is separate from its live puzzle. Browse Daily Puzzles for a different kind of short break.