operations · Year 3 · AC9M3A01
Inverse operations and fact families
Addition and subtraction undo each other, and so do multiplication and division. Three numbers make a fact family: 34 + 25 = 59 also tells you 59 − 25 = 34 and 59 − 34 = 25. To find a missing number, undo what was done: for ? − 38 = 45, add 38 back. For a puzzle with two steps, work backwards and undo the last step first.
Sample questions
Use 53 + 38 = 91. What is 91 − 53?
- The bar shows the whole 91 made of the parts 53 and 38.
- Take away one part and the other part is left: 91 − 53 = 38.
Answer: 38
Use 39 + 44 = 83. What is 83 − 44?
- The bar shows the whole 83 made of the parts 39 and 44.
- Take away one part and the other part is left: 83 − 44 = 39.
Answer: 39
Use 27 + 33 = 60. What is 60 − 33?
- The bar shows the whole 60 made of the parts 27 and 33.
- Take away one part and the other part is left: 60 − 33 = 27.
Answer: 27