Money Calculations
Learn to calculate change, create simple budgets and understand how GST works with Australian dollars and cents.
Australian Money
In Australia, we use dollars ($) and cents (c). There are 100 cents in one dollar. When we write money amounts, we use a decimal point to separate dollars from cents.
Our Coins and Notes
Did you know? Australia no longer uses 1c and 2c coins. Prices are rounded to the nearest 5 cents when paying with cash. This is called rounding.
Calculating Change
When you pay for something with more money than it costs, you get change back. To find the change, subtract the price from the amount you paid.
Change = Amount Paid − Cost of Item
Example: Shopping at the Canteen
Sandwich
$4.50
Juice Box
$2.00
Apple
$1.50
You buy: Sandwich ($4.50) + Juice ($2.00) = $6.50
You pay with: $10.00
Change: $10.00 − $6.50 = $3.50
Simple Budgets
A budget is a plan for how you will spend your money. It helps you decide what you can afford and how much you will have left over.
Example: Party Budget
Mia has $50.00 to spend on her birthday party. Here is her budget:
| Item | Cost |
|---|---|
| Cake | $18.00 |
| Decorations | $12.50 |
| Party bags | $9.00 |
| Drinks | $7.50 |
| Total | $47.00 |
Money left over: $50.00 − $47.00 = $3.00
Understanding GST
GST stands for Goods and Services Tax. In Australia, GST is 10% (10 cents for every dollar). Most things you buy already include GST in the price shown.
How GST Works
Price before GST
$10.00
GST (10%)
$1.00
Total price
$11.00
To find 10% of a price, simply divide by 10.
Tip: To calculate 10% of any amount, move the decimal point one place to the left. For example, 10% of $30.00 = $3.00.
Key Vocabulary
Change
The money returned to you when you pay more than the cost of an item.
Budget
A plan that shows how much money you have and how you will spend it.
GST
Goods and Services Tax — a 10% tax added to most purchases in Australia.
Decimal
A number with a decimal point separating whole dollars from cents (e.g. $5.75).
Worked Examples
You buy a book for $12.75 and pay with a $20 note. How much change do you get?
Step 1: Write the subtraction: $20.00 − $12.75
Step 2: Subtract cents: 100c − 75c = 25c
Step 3: Subtract dollars: $19 − $12 = $7
Answer: Change = $7.25
Jake has $25. He buys a hat for $14.50 and socks for $6.00. How much does he have left?
Step 1: Total spent: $14.50 + $6.00 = $20.50
Step 2: Money left: $25.00 − $20.50
Answer: Jake has $4.50 left.
A toy costs $20.00 before GST. What is the price including 10% GST?
Step 1: Calculate 10% of $20.00: $20.00 ÷ 10 = $2.00
Step 2: Add GST to the price: $20.00 + $2.00
Answer: Total price = $22.00
Knowledge Check
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Key Concepts Summary
- ●100 cents = 1 dollar. Use a decimal point to separate dollars and cents.
- ●Change = Amount paid − Cost of items.
- ●A budget helps you plan your spending and see if you have enough money.
- ●GST is 10% — divide the price by 10 to find the GST amount.
- ●Always line up the decimal points when adding or subtracting money.