Budgets/cost predictions | Year 6

01 / LEARN

Understand the idea.

List the costs before deciding

A budget sets how much money is available and plans how it will be used. List every required cost. When several identical items are bought, multiply the unit price by the quantity before adding that line to the total.

Compare the complete cost with the available money, rather than checking each item separately. A buffer is money kept unspent for uncertain costs. It is available if needed, but is not automatically another expense to add twice.

Update a prediction when something changes

Update the affected part when a price changes. If six items each cost fifty cents more, the total rises by $6 \times 0.50 = 3$ dollars. A fixed booking fee, however, is added once rather than once for every item.

For a stall, income is money collected and costs are money spent. The surplus is income minus all costs. An unused spending budget uses similar subtraction, but describes money remaining from an allowance rather than earnings from sales.

02 / WORKED EXAMPLES

See the method in action.

EXAMPLE 01

Worked example 1

A class has a picnic budget of 120 dollars. Its planned costs are shown. Find the total and the money left.

Planned picnic costs
Item	Cost in dollars
Snacks	18
Fruit	24
Drinks	30
Transport	35

Worked solution

1
Combine the food and drink costs.
$18 + 24 + 30 = 72 dollars$
Snacks, fruit and drinks are three separate planned costs.
2
Include transport.
$72 + 35 = 107 dollars$
The complete picnic total must include every row of the table.
3
Compare the total with the budget.
$120 - 107 = 13 dollars$
Subtracting planned spending from the available money finds what remains.
4
Interpret the remainder.
$107 < 120$
The plan fits the budget, with 13 dollars left for a buffer or later changes.

Answer

Total 107 dollars; 13 dollars left.

EXAMPLE 02

Worked example 2

A school stall collects 96 dollars. Materials cost 38.50 dollars and printing costs 12 dollars. Find its surplus.

Worked solution

1
Add all the stall’s costs.
$38.50 + 12.00 = 50.50 dollars$
Materials and printing both reduce the money kept from sales.
2
Subtract costs from income.
$96.00 - 50.50 = 45.50 dollars$
Surplus is the amount left after paying all the stated costs.
3
Check against the income.
$50.50 + 45.50 = 96.00$
Costs plus the 45.50-dollar surplus account for all money collected.

Answer

45.50 dollars surplus.

03 / YOUR TURN

Try it yourself.

Check your understanding

A budget is 50 dollars. Planned costs total 44 dollars. How much is left?

Show answer & reasoning

6 dollars.

$50 - 44 = 6$ dollars. This is the unused part of the spending budget after the planned costs are paid.

Keep practising

6 worksheet questions · 11 marks

Open worksheet Worked solutions

Read the questions online

A group has 100 dollars. It plans to spend 28, 35 and 16 dollars. Find the total and the amount left.
2 marks
Ten tickets cost 3.50 dollars each. Find their total cost.
1 mark
A fundraiser collects 84 dollars. Materials cost 31.60 dollars and printing costs 12.40 dollars. Find the surplus.
2 marks
A display needs eight packs at 2.75 dollars each and a stand costing 12.50 dollars. Find the total cost.
2 marks
Six lunches were planned at 3 dollars each. Their price rises to 3.50 dollars each. How much must be added to the budget?
2 marks
A class has a 10-dollar buffer. An extra delivery fee is 7 dollars. Explain whether the fee can be paid without removing a planned item.
2 marks

Read the worked solutions

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

A group has 100 dollars. It plans to spend 28, 35 and 16 dollars. Find the total and the amount left.
2 marks
$28 + 35 + 16 = 79$ ; $100 - 79 = 21$ .
Total 79 dollars; 21 dollars left.
Ten tickets cost 3.50 dollars each. Find their total cost.
1 mark
$3.50 \times 10 = 35$ .
35 dollars.
A fundraiser collects 84 dollars. Materials cost 31.60 dollars and printing costs 12.40 dollars. Find the surplus.
2 marks
Costs are $31.60 + 12.40 = 44$ ; $84 - 44 = 40$ .
40 dollars.
A display needs eight packs at 2.75 dollars each and a stand costing 12.50 dollars. Find the total cost.
2 marks
$8 \times 2.75 = 22$ ; $22 + 12.50 = 34.50$ .
34.50 dollars.
Six lunches were planned at 3 dollars each. Their price rises to 3.50 dollars each. How much must be added to the budget?
2 marks
Each rises by 0.50 dollars; $6 \times 0.50 = 3$ .
3 dollars.
A class has a 10-dollar buffer. An extra delivery fee is 7 dollars. Explain whether the fee can be paid without removing a planned item.
2 marks
$10 - 7 = 3$ , provided all other planned costs stay unchanged.
Yes; 3 dollars of the buffer remains.

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Curriculum reference & lesson scope

Australian Curriculum v9 and SA Curriculum Mathematics

Fraction/decimal/percentage quantities; discounts; budgets/cost predictions; comparing choices, risks and consequences.

Official curriculum source ↗

In this lesson

Understand the idea.

List the costs before deciding

Update a prediction when something changes

See the method in action.

Worked example 1

Combine the food and drink costs.

Include transport.

Compare the total with the budget.

Interpret the remainder.

Worked example 2

Add all the stall’s costs.

Subtract costs from income.

Check against the income.

Try it yourself.

Check your understanding

Keep practising