algebra · Year 4 · Suggested learning sequence
Number sentences with a missing number
The equals sign means both sides have the same value. To find a missing number, use the inverse operation: undo adding with subtracting, and undo multiplying with dividing. Check by putting your number in the box and reading the sentence. When there are numbers on both sides, work out the side you can, then make the other side match it.
Sample questions
What number goes in the box? 7 + □ = 9
- The box is the part that goes with 7 to make 9.
- Use the inverse: 9 − 7 = 2.
- 7 + 2 = 9, so the box is 2.
Answer: 2
What number goes in the box? 9 + □ = 12
- The box is the part that goes with 9 to make 12.
- Use the inverse: 12 − 9 = 3.
- 9 + 3 = 12, so the box is 3.
Answer: 3
What number goes in the box? 2 + □ = 11
- The box is the part that goes with 2 to make 11.
- Use the inverse: 11 − 2 = 9.
- 2 + 9 = 11, so the box is 9.
Answer: 9