Budgets and purchase decisions | Year 8

01 / LEARN

The idea, step by step

List the complete costs

A budget is a plan for money available, money spent and money kept. Start with the available amount. List each cost once and multiply unit prices by the number needed. Add delivery, booking or other fixed charges before judging whether the plan is affordable.

A useful budget separates needs from optional purchases and leaves room for unexpected costs when possible. An affordable option is not automatically the best choice: quality, safety, usefulness and reliability may matter too.

Compare whole plans

Compare alternatives for the same number of people or items. A cheaper advertised unit price may be cancelled out by a fee. A discount is only a saving if the final purchase meets the need and fits the budget.

Explain a recommendation using the numbers and the stated priorities. If information such as quality or transport cost is missing, identify that limitation rather than pretending the calculation settles every part of the decision.

A common trap

The cheapest unit price is always the cheapest final purchase.

Instead: Multiply by the required quantity and add fees before comparing. The total may tie or reverse.

02 / WORKED EXAMPLES

See the thinking

Example 1

A day-out budget

Maya has 100 AUD. Transport costs 18 AUD, food costs 32 AUD, and three tickets cost 12 AUD each. Find total spending and money left.

Tickets cost $3 \times 12 = 36$ AUD.
Total: $18 + 32 + 36 = 86$ AUD.
Remaining: $100 - 86 = 14$ AUD.

86 AUD spent; 14 AUD left.

Example 2

Include a fixed charge

Four meals cost 18 AUD each plus an 8 AUD delivery fee at A. At B, meals cost 20 AUD each with free delivery. Compare totals.

A costs $4 \times 18 + 8 = 80$ AUD.
B costs $4 \times 20 = 80$ AUD.
The prices tie; other relevant factors could decide.

Both cost 80 AUD for four meals.

Check your understanding

A budget is 75 AUD and planned costs total 62 AUD. How much remains?

Show answer

13 AUD

$75 - 62 = 13$ .

03 / WORKSHEET

Your turn

6 questions · 14 marks · Work at your own pace.

Worksheet PDF Worked solutions

Read the questions online

A student has 60 AUD and spends 17 AUD on travel and 26 AUD on food. Find the amount left.
2 marks
Five entries cost 9 AUD each plus one 5 AUD booking fee. Find the total.
2 marks
A 40 AUD bag has 15% off. A student has 35 AUD. Can they afford it, and what remains?
2 marks
Plan A costs 12 AUD per person plus 10 AUD once. Plan B costs 14 AUD per person. Compare costs for six people.
2 marks
An event budget is 150 AUD. Room hire is 65 AUD, food is 48 AUD, and equipment is 22 AUD. Find the remaining amount. Should an optional 18 AUD decoration purchase be added without changing the budget?
3 marks
A school group can buy 20 durable cups for 24 AUD or 20 single-use cups for 10 AUD. They have a 25 AUD budget and expect repeated events. Give a justified choice, including one assumption.
3 marks

Read the worked solutions

Equivalent correct methods earn the corresponding marks. Include units where asked.

A student has 60 AUD and spends 17 AUD on travel and 26 AUD on food. Find the amount left.
2 marks
Total cost: $17 + 26 = 43$ .
Remaining: $60 - 43 = 17$ .
17 AUD
Five entries cost 9 AUD each plus one 5 AUD booking fee. Find the total.
2 marks
$5 \times 9 + 5 = 50$ .
50 AUD
A 40 AUD bag has 15% off. A student has 35 AUD. Can they afford it, and what remains?
2 marks
$40 \times 0.85 = 34$ .
$35 - 34 = 1$ .
Yes; final price 34 AUD and 1 AUD remains.
Plan A costs 12 AUD per person plus 10 AUD once. Plan B costs 14 AUD per person. Compare costs for six people.
2 marks
A: $6 \times 12 + 10 = 82$ .
B: $6 \times 14 = 84$ .
A: 82 AUD; B: 84 AUD; A is 2 AUD cheaper.
An event budget is 150 AUD. Room hire is 65 AUD, food is 48 AUD, and equipment is 22 AUD. Find the remaining amount. Should an optional 18 AUD decoration purchase be added without changing the budget?
3 marks
Total: $65 + 48 + 22 = 135$ .
Remaining: $150 - 135 = 15$ .
Adding 18 gives total 153 AUD.
15 AUD remains; no, the extra purchase would exceed the budget by 3 AUD.
A school group can buy 20 durable cups for 24 AUD or 20 single-use cups for 10 AUD. They have a 25 AUD budget and expect repeated events. Give a justified choice, including one assumption.
3 marks
Both initial purchases fit the budget.
Durable cups leave $25 - 24 = 1$ AUD; single-use cups leave 15 AUD.
The durable option may reduce repeated purchases, assuming safe reuse and cleaning; price alone does not decide.
Either justified decision is accepted; durable cups fit the budget and may be preferable if reused enough and cleaning is available.

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Curriculum reference & lesson scope

Australian Curriculum v9 / SA Curriculum

Percentage increase/decrease; finding an original amount; discounts and mark-ups; percentage comparisons; budgets and purchase decisions; modelling and checking financial problems with digital tools. Simple interest can be offered here as a school-dependent application and developed in Year 9.

Official curriculum source ↗

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