The idea, step by step
Make a cost model
A model is a simpler way to represent a situation. A list or table of quantities and prices helps you choose calculations. If one notebook costs 4 dollars, three notebooks cost 3 × 4 = 12 dollars.
Distinguish the price of one item from the total for several. Add other costs after finding each group cost. Read whether a fee is charged once or once for every item; this changes the calculation.
Work through and check
For a multi-step problem, write a short plan before calculating. To find change, work out the full cost and then subtract it from the money paid. To find how much more is needed, compare the cost with the money available.
Label each result in dollars. Check by reversing the last step: cost plus change should equal money paid. If the total is larger than the budget, report a shortage rather than a negative amount of change.
A common trap
I multiplied the once-only delivery fee by the number of items.
Instead: Find what each price refers to. A single delivery fee is added once after the item costs.
See the thinking
Buy groups of items
A class buys 4 books at 7 dollars each and one poster for 6 dollars. It pays with 40 dollars. Find the change.
- Books: 4 × 7 = 28 dollars.
- Total: 28 + 6 = 34 dollars.
- Change: 40 − 34 = 6 dollars. Check 34 + 6 = 40.
Allow for a once-only fee
A club orders 6 badges at 3 dollars each. Delivery costs 5 dollars for the whole order. The club has 20 dollars. How much more does it need?
- Badges cost 6 × 3 = 18 dollars.
- Add delivery once: 18 + 5 = 23 dollars.
- The shortage is 23 − 20 = 3 dollars.
Check your understanding
Five pens cost 2 dollars each. One folder costs 4 dollars. What is the total?
Show answer
14 dollars
5 × 2 = 10 dollars for pens; 10 + 4 = 14 dollars altogether.
Your turn
6 questions · 12 marks · Work at your own pace.
Read the questions online
- Three rulers cost 4 dollars each. Find the total.1 mark
- Four tickets cost 6 dollars each. A group booking fee is 3 dollars once. Find the full cost.2 marks
- A student pays 30 dollars for 3 packs costing 8 dollars each. Find the change.2 marks
- A class needs 8 pots costing 5 dollars each. It has 36 dollars. How much more is needed?2 marks
- Complete the group costs and the grand total.3 marks
Class project purchases Item Quantity Price each Bags 3 6 dollars Labels 4 2 dollars - Nia buys 2 games at 9 dollars each and pays one delivery fee of 4 dollars. She says the total is 26 dollars. Identify the likely mistake and correct it.2 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Three rulers cost 4 dollars each. Find the total.1 mark
3 × 4 = 12.
12 dollars - Four tickets cost 6 dollars each. A group booking fee is 3 dollars once. Find the full cost.2 marks
4 × 6 = 24.
24 + 3 = 27.
27 dollars - A student pays 30 dollars for 3 packs costing 8 dollars each. Find the change.2 marks
3 × 8 = 24.
30 − 24 = 6.
6 dollars - A class needs 8 pots costing 5 dollars each. It has 36 dollars. How much more is needed?2 marks
8 × 5 = 40.
40 − 36 = 4.
4 dollars - Complete the group costs and the grand total.3 marks
Class project purchases Item Quantity Price each Bags 3 6 dollars Labels 4 2 dollars 3 × 6 = 18; 4 × 2 = 8.
18 + 8 = 26.
Bags 18 dollars; labels 8 dollars; total 26 dollars. - Nia buys 2 games at 9 dollars each and pays one delivery fee of 4 dollars. She says the total is 26 dollars. Identify the likely mistake and correct it.2 marks
2 × 9 = 18.
The once-only fee gives 18 + 4 = 22, not 18 + 8.
She added delivery twice. The total is 22 dollars.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics 2026
Estimating transactions; multi-step models; responsible purchases; class enterprise and community effects.
Official curriculum source ↗