Modelling purchases | Year 3

01 / LEARN

The idea, step by step

Make a small purchase plan

First decide what is bought and how much each item costs. Add different prices. For several identical items, use equal groups or multiplication.

Use the same money unit. For example, 1 dollar 20 cents becomes 120 cents. A quick estimate helps you notice an answer that is much too large or too small.

A school stall price list for the examples
Item	Price
Bookmark	50 cents
Pencil	85 cents
Eraser	40 cents

Check the money and change

Compare the total cost with the money available before buying. If the cost is greater, choose fewer items or a different plan.

When the money is enough, subtract the cost to find change. Check by adding the cost and change: they should rebuild the amount paid.

A common trap

Add dollars and cents as if they were the same unit.

Instead: Name all amounts in cents, or keep dollars and cents clearly separate before calculating.

02 / WORKED EXAMPLES

See the thinking

Example 1

Several identical items

Buy 3 bookmarks at 50 cents each. Pay with 2 dollars. What change should you receive?

Three bookmarks cost $3 \times 50 = 150$ cents.
2 dollars are 200 cents, so change is $200 - 150 = 50$ cents.
Check: $150 + 50 = 200$ cents.

50 cents change.

Example 2

Different items

A pencil costs 85 cents and an eraser costs 40 cents. Find the total and the change from 2 dollars.

Add the prices: $85 + 40 = 125$ cents.
Subtract from 200 cents: $200 - 125 = 75$ cents.

Total 1 dollar 25 cents; change 75 cents.

Check your understanding

Two items cost 60 cents each. Are 2 dollars enough? What change remains?

Show answer

Yes; 80 cents change.

$2 \times 60 = 120$ cents; $200 - 120 = 80$ cents.

03 / WORKSHEET

Your turn

6 questions · Work at your own pace.

Worksheet PDF Worked solutions

Read the questions online

A sticker costs 20 cents. What do 4 stickers cost?
A notepad costs 1 dollar 20 cents. A pencil costs 50 cents. Find the total.
A bookmark costs 75 cents. Find the change from 1 dollar.
Two folders cost 1 dollar each. Can 1 dollar 80 cents pay for both?
A child buys an 80-cent pen and a 35-cent eraser. They pay 2 dollars and receive 85 cents change. Check the change.
You have 2 dollars. Cards cost 60 cents each. What is the greatest number you can buy, and what money remains?

Read the worked solutions

A sticker costs 20 cents. What do 4 stickers cost?
$4 \times 20 = 80$ .
80 cents.
A notepad costs 1 dollar 20 cents. A pencil costs 50 cents. Find the total.
$120 + 50 = 170$ cents.
1 dollar 70 cents.
A bookmark costs 75 cents. Find the change from 1 dollar.
$100 - 75 = 25$ cents.
25 cents.
Two folders cost 1 dollar each. Can 1 dollar 80 cents pay for both?
Both cost 200 cents. $200 - 180 = 20$ cents.
No; it is 20 cents short.
A child buys an 80-cent pen and a 35-cent eraser. They pay 2 dollars and receive 85 cents change. Check the change.
$80 + 35 = 115$ cents; $115 + 85 = 200$ cents.
It is correct.
You have 2 dollars. Cards cost 60 cents each. What is the greatest number you can buy, and what money remains?
$3 \times 60 = 180$ cents; $200 - 180 = 20$ . Four cost 240 cents, which is too much.
3 cards, with 20 cents remaining.

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Needs and wants

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Curriculum reference & lesson scope

Australian Curriculum v9 and SA Curriculum Mathematics

Dollars/cents; equivalent amounts; modelling purchases; needs/wants; class enterprise and others' wellbeing.

Official curriculum source ↗

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