Understand the idea.
Add every required cost
A budget is the amount available for a plan. List each required cost, including fees, and add them using consistent money units. Subtract the total spending from the budget to find what remains; a negative result means the plan exceeds the budget.
Distinguish compulsory spending from optional extras. Test an extra purchase against the money left after required costs, then recalculate the revised total. A plan using exactly the budget is affordable but leaves no money for further costs.
| Item | Cost in dollars |
|---|---|
| Sandwiches | 24 |
| Drinks | 16 |
| Fruit | 12 |
Compare a fair amount
Compare offers using the same quantity. A cheaper pack may contain fewer items. Find how many whole packs are required, calculate their total prices, and check that each option supplies the requested number without an unnoticed shortfall.
A cost per item helps compare value, but the question may require a fixed number or allow only whole packs. Explain whether your decision minimises total spending, price per item or waste; these aims do not always select the same purchase.
See the method in action.
Check a picnic plan
A picnic costs 24 dollars for sandwiches, 16 dollars for drinks and 12 dollars for fruit. The budget is 60 dollars. How much remains? Can two extra fruit packs costing 4 dollars each be added?
| Item | Cost in dollars |
|---|---|
| Sandwiches | 24 |
| Drinks | 16 |
| Fruit | 12 |
Worked solution
- 1
Add the required picnic costs.
Sandwiches, drinks and fruit must all be included in the initial plan.
- 2
Find the unspent budget.
Subtracting spending from the budget gives the amount available for extras.
- 3
Price the two extra packs.
Each pack costs four dollars, and two packs are requested.
- 4
Check the revised plan.
The extras use exactly the remaining eight dollars, so both fit the budget.
8 dollars remains; both packs can be added.
Compare a common quantity
A pack of 4 pens costs 3.60 dollars. A pack of 6 pens costs 4.80 dollars. Which option is cheaper when buying exactly 12 pens?
Worked solution
- 1
Find how many four-packs are needed.
Three whole four-packs provide exactly twelve pens.
- 2
Find how many six-packs are needed.
Two whole six-packs also provide exactly twelve pens.
- 3
Compare the equal quantities.
Two six-packs cost less and save one dollar twenty for the same twelve pens.
Two 6-packs, costing 9.60 dollars.
Try it yourself.
Check your understanding
A 35-dollar budget pays for items costing 12.80 and 9.60 dollars. What remains?
Show answer & reasoning
12.60 dollars
Add the purchases first: dollars. The remainder is dollars, keeping the decimal points aligned.
Keep practising
6 worksheet questions · 16 marks
Read the questions online
- A group has 80 dollars. Food costs 32.50 dollars and transport costs 28 dollars. Find the money left.2 marks
- Buy exactly 10 pencils: packs of 2 cost 1.40 dollars, or packs of 5 cost 3 dollars. Which option costs less?3 marks
- You spend of a 50-dollar budget on food and another 18 dollars on travel. What remains?3 marks
- A game costs 26 dollars online plus 6 dollars delivery, or 31 dollars in a local shop. Which total is lower?2 marks
- Exactly 12 people need transport. Option A costs a flat 60 dollars; option B costs 6 dollars per person. Both have enough seats. Compare costs.3 marks
- A class has 100 dollars. It needs 8 art kits at 9.50 dollars each and a 12-dollar delivery. Can it also buy a 15-dollar poster?3 marks
Read the worked solutions
Equivalent correct methods earn the corresponding marks. Include units where asked.
- A group has 80 dollars. Food costs 32.50 dollars and transport costs 28 dollars. Find the money left.2 marks
Total spending is 60.50 dollars; subtract from 80.
19.50 dollars - Buy exactly 10 pencils: packs of 2 cost 1.40 dollars, or packs of 5 cost 3 dollars. Which option costs less?3 marks
Five 2-packs cost 7 dollars; two 5-packs cost 6 dollars.
Two 5-packs cost 6 dollars, saving 1 dollar. - You spend of a 50-dollar budget on food and another 18 dollars on travel. What remains?3 marks
Food costs 15 dollars; total spending is 33 dollars.
dollars.
17 dollars - A game costs 26 dollars online plus 6 dollars delivery, or 31 dollars in a local shop. Which total is lower?2 marks
dollars; dollars.
The local shop, by 1 dollar. - Exactly 12 people need transport. Option A costs a flat 60 dollars; option B costs 6 dollars per person. Both have enough seats. Compare costs.3 marks
Option B: .
dollars.
A costs 60 dollars and B costs 72 dollars; A saves 12 dollars. - A class has 100 dollars. It needs 8 art kits at 9.50 dollars each and a 12-dollar delivery. Can it also buy a 15-dollar poster?3 marks
Kits and delivery cost dollars.
Adding the poster gives 103 dollars.
No; it would exceed the budget by 3 dollars.
Curriculum reference & lesson scope
Australian Curriculum v9 / SA Curriculum Mathematics
Fractions–decimals–percentages; percentages of quantities; expressing one amount as a percentage of another; discounts and sale prices; practical spending/budget comparisons; choosing and explaining a financial model.
Official curriculum source ↗