The idea, step by step
Read the price and unit
A price tells how much money is needed for an item. First check that the prices use the same unit. Here both prices are in dollars. A 4-dollar notebook costs less than a 7-dollar notebook.
| Item | Price in dollars |
|---|---|
| Plain notebook | 4 |
| Patterned notebook | 7 |
Find the difference
To find how much more, compare the two prices. Count from the lower price to the higher price, or subtract. From 4 to 7 is 3, so the 7-dollar notebook costs 3 dollars more. A lower price does not tell us everything about which item someone needs.
A common trap
Saying a more expensive item is always the better choice.
Instead: The price tells the cost. We also need to know what the item must do and whether it is suitable.
See the thinking
Find a lower price
A red cap costs 9 dollars and a blue cap costs 6 dollars. Which costs less, and by how much?
- 6 is less than 9, so the blue cap costs less.
- 9 − 6 = 3.
Equal prices
Two different rulers each cost 2 dollars. Is one cheaper?
- Both prices are 2 dollars.
- Their difference is 2 − 2 = 0.
Check your understanding
A pencil case costs 8 dollars and a pouch costs 5 dollars. How much more is the pencil case?
Show answer
3 dollars.
Count 5 to 8, or subtract 8 − 5.
Your turn
6 questions · Work at your own pace.
Read the questions online
- A green pen costs 2 dollars. A purple pen costs 3 dollars. Which costs less?
- A ball costs 12 dollars and a skipping rope costs 9 dollars. Which costs more?
- One book costs 7 dollars and another costs 10 dollars. What is the price difference?
- Two glue sticks each cost 4 dollars. What is the difference in their prices?
- Put these prices in order from lowest to highest: 8 dollars, 3 dollars, 6 dollars.
- A drawing pad costs 6 dollars and a notebook costs 9 dollars. Sam says the notebook costs 15 dollars more. Explain the mistake.
Read the worked solutions
- A green pen costs 2 dollars. A purple pen costs 3 dollars. Which costs less?
2 dollars is less than 3 dollars.
The green pen. - A ball costs 12 dollars and a skipping rope costs 9 dollars. Which costs more?
12 is greater than 9.
The ball. - One book costs 7 dollars and another costs 10 dollars. What is the price difference?
10 − 7 = 3.
3 dollars. - Two glue sticks each cost 4 dollars. What is the difference in their prices?
4 − 4 = 0.
0 dollars. - Put these prices in order from lowest to highest: 8 dollars, 3 dollars, 6 dollars.
Compare the numbers 3, 6 and 8.
3 dollars, 6 dollars, 8 dollars. - A drawing pad costs 6 dollars and a notebook costs 9 dollars. Sam says the notebook costs 15 dollars more. Explain the mistake.
How much more asks for 9 − 6, not 9 + 6.
Sam added the prices. The difference is 3 dollars.
Curriculum reference & lesson scope
Australian Curriculum v9 and SA Curriculum Mathematics
Comparing prices; $1/$2 coins and notes; purchases; limited money and saving; needs/wants; consumer choices.
Official curriculum source ↗