The idea, step by step
Read the model
The top circle in this model is the whole. The two lower circles are parts. Join the parts to find the whole.
For example, a whole of fourteen can have parts nine and five. The lines mean the parts belong to that whole.
A blank changes the question
If the whole is blank, add the parts. If one part is blank, find what joins the known part to make the whole.
You can count on from the known part to the whole. You can also start with the whole and take away the known part.
A common trap
Adding the whole and a part to find the other part.
Instead: The whole already contains both parts. Find the missing part by counting on or subtracting.
See the thinking
Read the complete model
The whole is fourteen. One part is nine. What is the other part?
- Keep nine as the known part.
- Count from nine to fourteen: ten, eleven, twelve, thirteen, fourteen.
- Five more were needed.
Find a whole
The two parts are eight and seven. Find the whole.
- Join eight counters and seven counters.
- Eight and two make ten, with five more left.
- The whole is fifteen.
Check your understanding
A whole is twelve. Its parts are ten and a blank. What is the blank?
Show answer
2
Ten and two make twelve.
Your turn
6 questions · Work at your own pace.
Read the questions online
- The parts are four and six. What is the whole?
- The whole is eleven. One part is eight. Find the other part.
- The whole is eighteen. One part is ten. Find the other part.
- Draw a part–whole model for parts seven and five.
- A model has whole sixteen and parts nine and six. Is it correct? Explain.
- Choose two different parts for a whole of thirteen.
Read the worked solutions
- The parts are four and six. What is the whole?
4 + 6 = 10.
10 - The whole is eleven. One part is eight. Find the other part.
8 + 3 = 11.
3 - The whole is eighteen. One part is ten. Find the other part.
Ten and eight make eighteen.
8 - Draw a part–whole model for parts seven and five.
7 + 5 = 12; label the whole and both parts.
A whole of 12 with parts 7 and 5. - A model has whole sixteen and parts nine and six. Is it correct? Explain.
The parts must add to the whole.
No. Nine and six make fifteen, not sixteen. - Choose two different parts for a whole of thirteen.
6 + 7 = 13. Accept any two whole-number parts totalling thirteen.
For example, six and seven.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Year 1 additive situations and number bonds within twenty.
Official curriculum source ↗