Subtraction Mathdoku Custom Subtraction 9×9 Small — Set 21
| 19+ | 15+ | 19+ | 1- | 6= | ||||
| 16+ | 3- | 13+ | 12+ | |||||
| 1= | 15+ | 6=6 | 5= | 3 | ||||
| 3- | 15+ | 7= | 5+ | 7- | 5= | |||
| 7 | 9+6 | 1- | 1 | 3 | 6+2 | |||
| 3= | 22+6 | 16+ | 2- | 4=4 | ||||
| 4+ | 8= | 4= | 7=7 | |||||
| 5= | 15+ | 4=4 | 1= | 2= | 8= | |||
| 11+ | 14+ | 4- | 12+ | 1 | 22+ |
Show solution
| 2 | 7 | 8 | 3 | 9 | 5 | 4 | 6 | 1 |
| 9 | 5 | 2 | 1 | 7 | 6 | 3 | 4 | 8 |
| 8 | 9 | 1 | 4 | 2 | 7 | 6 | 5 | 3 |
| 4 | 1 | 6 | 7 | 3 | 8 | 9 | 2 | 5 |
| 7 | 6 | 9 | 8 | 5 | 4 | 1 | 3 | 2 |
| 1 | 2 | 3 | 6 | 8 | 9 | 5 | 7 | 4 |
| 3 | 8 | 4 | 5 | 1 | 2 | 7 | 9 | 6 |
| 6 | 3 | 5 | 9 | 4 | 1 | 2 | 8 | 7 |
| 5 | 4 | 7 | 2 | 6 | 3 | 8 | 1 | 9 |
Solver Notes
Frequently Asked Questions
What is Custom Mathdoku?
Mathdoku (also known as KenKen or Calcudoku) is a math-based logic puzzle. You fill a subtraction grid so every row and column contains each digit exactly once (like sudoku), and every boldly outlined cage satisfies its arithmetic clue — the digits inside the cage must produce the target number using the specified operation (+, −, ×, or ÷). The custom Mathdoku variant uses custom as the primary operation, giving extra practice with that specific arithmetic skill.
How do I solve medium subtraction Mathdoku?
Start with 1-cell cages (the digit is already given) and small cages with few valid combinations. Use the Latin square rule (no repeats per row/column) to eliminate candidates. For medium puzzles, alternate between checking cage combinations and applying row/column constraints until every cell is resolved. Division cages are often the most constraining — use them first.
What grade level is Mathdoku best for?
This puzzle is well suited for elementary and middle school students. 4×4 addition Mathdoku is accessible from Grade 2. 6×6 puzzles with all four operations target Grades 4–6. 9×9 expert puzzles challenge advanced middle schoolers and adults. Teachers use Mathdoku as a differentiated activity — match the grid size and operations to the student’s current arithmetic fluency.
How many operations does Custom Mathdoku use?
Classic Mathdoku uses all four arithmetic operations (+, −, ×, ÷) distributed across cages. More operations increase solving complexity, as each cage type narrows candidates differently.
What is the difference between Mathdoku and Kakuro?
Both are arithmetic logic puzzles, but they differ in structure. Mathdoku (like sudoku) ensures each digit appears exactly once per row and column across the whole grid. Kakuro uses run-based clues where digits in each run must sum to a target without repetition within that run, but the same digit can appear in different runs. Mathdoku is generally better for classroom arithmetic practice; Kakuro rewards mastering addition combination sets.