Understand the idea.
Build a small model
A model turns a real situation into quantities and calculations. For a purchase, write down the number of items, the price of each and any extra charge. Decide which charges repeat before choosing operations.
Multiply for equal-priced items, then add any fee charged once for the whole order. Keep different items on separate lines so that a ticket price cannot accidentally be treated as a group fee.
Check what the answer means
Ask what the question wants: the total cost is the amount spent; change is the part of a payment returned. Find the cost before subtracting it from the money handed over.
Check your model against the story and a rough estimate. State important assumptions, such as everyone paying the same ticket price. If a price or the group size changes, update that part of the calculation.
See the method in action.
One fee for the group
Six students pay 4 dollars each to enter a garden. There is one 5-dollar group booking fee. Find the total.
Worked solution
- 1
Find the six ticket costs.
Each of the six students pays the same 4-dollar price.
- 2
Add the booking fee once.
The 5-dollar fee belongs to the whole group, rather than to each ticket.
- 3
Check the model against the order.
The calculation includes all six entries and exactly one group fee.
29 dollars
Find the change
Buy 3 packs of pencils at 7 dollars each and pay with 30 dollars. Find the change.
Worked solution
- 1
Find the price of three packs.
Multiplication combines three equal pack prices.
- 2
Subtract the cost from the payment.
Change is the money paid beyond the purchase cost.
- 3
Check the payment is accounted for.
The shop keeps the cost and returns the rest.
9 dollars
Try it yourself.
Check your understanding
Four bags cost 6 dollars each. Delivery for the whole order is 3 dollars. Find the total.
Show answer & reasoning
27 dollars
The bags cost dollars. Delivery is charged once, so the total is dollars.
Keep practising
6 worksheet questions · 14 marks
Read the questions online
- Five notebooks cost 3 dollars each. Find the cost.2 marks
- Three tickets cost 8 dollars each. Add one 4-dollar booking fee.2 marks
- An order costs 37 dollars. Pay with 50 dollars. Find the change.2 marks
- Use the prices to find the total for 4 brushes and 2 trays.3 marks
Art-shop prices Item One costs (dollars) Brush 4 Paint tray 5 - A trip model is dollars. The 8 means eight students. Explain what the 5 and 6 could mean.2 marks
- Mina says 9 tickets at 4 dollars each cost 396 dollars. Give a quick check that shows this is unreasonable.3 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- Five notebooks cost 3 dollars each. Find the cost.2 marks
.
15 dollars - Three tickets cost 8 dollars each. Add one 4-dollar booking fee.2 marks
Tickets: .
.
28 dollars - An order costs 37 dollars. Pay with 50 dollars. Find the change.2 marks
.
Check: .
13 dollars - Use the prices to find the total for 4 brushes and 2 trays.3 marks
Art-shop prices Item One costs (dollars) Brush 4 Paint tray 5 Brushes: dollars.
Trays: dollars.
.
26 dollars - A trip model is dollars. The 8 means eight students. Explain what the 5 and 6 could mean.2 marks
represents eight equal fares.
The 6 is added once, so it can represent a group fee.
Accept another consistent explanation.
Each student pays 5 dollars and the group pays one 6-dollar extra charge. - Mina says 9 tickets at 4 dollars each cost 396 dollars. Give a quick check that shows this is unreasonable.3 marks
.
.
396 is far larger than the estimate.
Ten tickets cost 40 dollars, so nine must cost less than 40 dollars. The exact cost is 36 dollars.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics 2026
Practical models; immediate/future financial plans; consumer goals; ethical/sustainable choices.
Official curriculum source ↗