Money
🎯 In this topic you will
- Use the decimal point to represent two different units of money within the same amount.
- Add amounts of money and use the total to calculate the correct change.
- Subtract amounts of money to determine the change accurately.
🧠 Key Words
- buy
- change
- decimal point
- spend
Show Definitions
- buy: To pay money in order to receive goods or services.
- change: The amount of money returned when the amount paid is more than the cost.
- decimal point: The symbol used to separate whole units of money from parts of a unit, such as pounds and pence.
- spend: To use money to pay for something.
Working with Money Correctly
A dding and subtracting money follows the same rules as adding and subtracting numbers. However, you must always pay attention to the currency units when you calculate. Different units, such as dollars and cents, cannot be treated as the same. For example, subtracting 5 cents from 5 dollars does not leave you with no money, because the units are different.
💡 Quick Math Tip
Check the units: When adding or subtracting money, always make sure the units match. Dollars and cents are different units, so you cannot treat them as the same number. For example, subtracting cents from dollars does not cancel the amount unless both are written in the same unit.
❓ EXERCISES
1. Write each amount using a decimal point.
| Using dollars and cents | Using a decimal point |
|---|---|
| $4$ and $50$c | |
| $8$ and $70$c | |
| $24$ and $5$c | |
| $10$ | |
| $99$c |
👀 Show answer
2. How many dollars and cents are there in each of these amounts?
| Using dollars and cents | Using a decimal point |
|---|---|
| $20.45$ | |
| $9.75$ | |
| $15.00$ | |
| $2.09$ | |
| $0.30$ |
👀 Show answer
3. Use a decimal point to write each amount of money in dollars and cents.
👀 Show answer
b. $80.00$
c. $0.95$
d. $0.08$
🧠 Think like a Mathematician
Zara has two different banknotes and two different coins in her pocket.
How much money could she have?
What is the greatest amount of money that she could have?
What is the smallest amount of money that she could have?
👀 Show answer
- Possible amount: One example is using $20$ and $10$ banknotes, and $25$c and $10$c coins, giving a total of $30.35$.
- Greatest amount: Using the two largest different banknotes ($20$ and $10$) and the two largest different coins ($25$c and $10$c) gives $30.35$.
- Smallest amount: Using the two smallest different banknotes ($10$ and $5$) and the two smallest different coins ($1$c and $2$c) gives $15.03$.
❓ EXERCISES
4. Sumi and Virun visit the school shop.
a. Sumi has $50$c. She buys a pencil and an eraser. How much does she spend? How much change will she get?
b. Virun has $90$c. He buys two highlighter pens. How much does he spend? How much change will he get?
👀 Show answer
b. $37$c $+$ $37$c $=$ $74$c, change $=$ $90$c $-$ $74$c $=$ $16$c.
5.
a. Jamila buys a coffee, a soda and a milkshake with $10$. How much does she spend? How much change will she get?
b. Liam has $5$ to spend on two drinks. He does not like coffee. What could he buy? What change would he get?
👀 Show answer
b. One example: tea ($2.00$) and soda ($1.10$) cost $3.10$, change $= 5.00 - 3.10 = 1.90$.
6. Two ice creams cost $8$. How much does one ice cream cost? Write your number sentence and solve it to find the cost of an ice cream.
👀 Show answer
7. Priya pays for her trainers with a $50$ note. She gets $17$ change. How much do the trainers cost? Write your number sentence and solve it to find the cost of the trainers.
👀 Show answer
8. Xiumin has $6.50$. He buys a comic and gets $1.20$ change. How much does the comic cost? Write your number sentence and solve it to find the cost of the comic.
👀 Show answer
9. Isha writes the calculation $50 - \Box = 21$. Write a problem to match Isha’s number sentence.