Moocsoft.net · Free website worksheet
Missing Number Puzzles
Five original questions · Separate answer key
- Write the missing value and one line explaining your method for each question.
- Use the stated rule or rule family consistently across every row.
- Try the question sheet before turning to the separate answer key. There is no time limit.
- These are original website practice examples, not solutions to numbered app levels.
1. Complete a balanced equation
What number belongs in the box?
Rule: Use ordinary addition and the operation that reverses adding 18.
2. Find the repeated row total
Complete the last row using the same addition rule.
Rule: Add the first number to the second number to get the result.
| First number | Second number | Result |
|---|---|---|
| 6 | 9 | 15 |
| 8 | 5 | 13 |
| 7 | 12 |
3. Multiply, then make one adjustment
Multiply the first two numbers, then find the same subtraction used in both complete rows.
Rule: Use multiplication followed by one constant subtraction.
| First number | Second number | Result |
|---|---|---|
| 3 | 4 | 10 |
| 5 | 3 | 13 |
| 6 | 4 |
4. Recover the missing input
The blank is the second input. Work backward from the final result using the stated rule.
Rule: Result = first number × second number + first number.
| First number | Second number | Result |
|---|---|---|
| 2 | 5 | 12 |
| 3 | 4 | 15 |
| 4 | 28 |
5. Compare two squared values
Complete the last row by subtracting the second square from the first square.
Rule: Square each input separately, then subtract: first² − second².
| First number | Second number | Result |
|---|---|---|
| 5 | 3 | 16 |
| 7 | 4 | 33 |
| 9 | 5 |
Free website practice sheet. It is separate from the Math Riddles app and does not connect to or import into the app.
Guide: moocsoft.net/guides/missing-number-puzzles-with-answers/
Moocsoft.net · Separate answer key
Missing-number answers and checks
Compare your method with the stated rule, then substitute your answer back into every row.
1. Complete a balanced equation Answer: 29
Subtract 18 from both sides: 47 − 18 = 29. Substitute 29 into the original equation to check your answer.
- 29 + 18 = 47.
2. Find the repeated row total Answer: 19
The first two numbers add to the result in every row. Apply the same rule to the final row: 7 + 12 = 19.
- 6 + 9 = 15.
- 8 + 5 = 13.
- 7 + 12 = 19.
3. Multiply, then make one adjustment Answer: 22
Each result is the product of the first two numbers minus 2. The final row is (6 × 4) − 2 = 22. Subtract after multiplying; subtracting 2 from an input would change the grouping.
- (3 × 4) − 2 = 10.
- (5 × 3) − 2 = 13.
- (6 × 4) − 2 = 22.
4. Recover the missing input Answer: 6
The final row means 4 × □ + 4 = 28. Subtract 4 to get 4 × □ = 24, then divide by 4 to get 6. Put 6 back into the original rule to check it.
- 2 × 5 + 2 = 12.
- 3 × 4 + 3 = 15.
- 4 × 6 + 4 = 28.
5. Compare two squared values Answer: 56
Square both inputs separately. In the final row, 9² − 5² = 81 − 25 = 56. Squaring the difference would be a different operation: (9 − 5)² = 16.
- 5² − 3² = 25 − 9 = 16.
- 7² − 4² = 49 − 16 = 33.
- 9² − 5² = 81 − 25 = 56.
These original examples are website practice, not answers to numbered app levels. Explore the current app at moocsoft.net/math-riddles/.