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Number Puzzles Calculator

Online working-backwards number puzzle. Enter the result c and coefficients for the rule “multiply by a, add b gives c”, and it reverses the steps to recover the original number—great for elementary algebra and reverse-reasoning drills.

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Original=(c−b)/a
x×a +bc← 逆推还原
Multiplier
Added
Result

📖 Tutorial | Number Puzzle

1. Definition
Undo the operations from the result to recover the unknown.
2. Formula & Notation
InverseAdd→subtract, multiply→divide
OrderUndo the last first
3. Properties & Laws
  • Original=(c−b)/a;
  • Work backward;
  • Use parentheses;
  • Check by substitution.
4. Steps
  1. Enter a, b, c;
  2. Click "Find Original";
  3. Or click "Load Example".
5. Worked Examples
Example: times 3 plus 8 is 35.
Solution: original 9.
6. Common Pitfalls
Last undone first;
Multiplier nonzero;
Add-first differs.

❓ FAQ | Number Puzzle

Working backwards?
Inverse operations.
×3+8=35?
9.
Order?
Last first.
Add first?
Divide then subtract.
Confirm?
Gives 35.
Multiplier 0?
Cannot undo.