ACARA v9 CONTENT DESCRIPTION “solve problems involving purchases and the calculation of change to the nearest five cents, and estimate solutions to money problems by rounding”
Money is the most familiar place decimals appear: dollars and cents, with two decimal places for the cents. Adding two amounts of money is just decimal addition with a dollar sign — line up the decimal points and add, so $2.50 plus $1.30 is $3.80. Everything learned about tenths, hundredths and decimal place value applies directly to money, which is why money is the context Year 4 uses to make the arithmetic real. Handling money well means handling decimals well, in the situations a child meets every time they shop.
Adding money
Add amounts of money by lining up the decimal points and adding.
Add $2.50 and $1.30. Line up the dollars and cents.
Working out change
Change is what is given back when you pay more than something costs, and it is found by subtracting the cost from the amount paid. Pay $5.00 for an item costing $3.60 and the change is $1.40, because $5.00 take away $3.60 leaves $1.40. Making change is everyday subtraction with money, and counting up from the cost to the amount paid is a handy way to find it. Knowing how much change to expect is a practical skill that guards against being short-changed and builds a feel for how amounts of money relate.
Making change
Change is the amount paid minus the cost, found by subtracting.
You pay $5.00 for an item costing $3.60. How much change?
Estimating with rounding
Often an exact total is not needed, only a rough idea, and rounding to the nearest dollar gives it fast. $4.99 is about $5, because ninety-nine cents rounds up; $3.20 is about $3, because twenty cents rounds down. Estimating a total by rounding each amount tells you roughly what the shopping will cost, and it is a quick check that an exact answer is sensible. The rule is the decimal rounding already learned: fifty cents or more rounds up, less rounds down. Estimation is a real-world skill, used far more often than exact calculation.
Rounding money
Round money to the nearest dollar: 50 cents or more rounds up.
About how many dollars is $4.99? Round to the nearest dollar.
Paying for several
When several items cost the same, the total is multiplication, not repeated addition by hand. Three apples at $1.20 each cost three times $1.20, which is $3.60. Seeing repeated cost as multiplication connects money back to the times tables: the price is the group size and the number of items is the multiplier. This is faster and less error-prone than adding the same price again and again, and it is exactly the kind of problem — buying several of the same thing — that comes up constantly in real shopping.
Repeated cost
The cost of several items at the same price is found by multiplying.
3 items cost $1.20 each. What is the total?
Is there enough?
A common money question is not the exact total but simply whether you have enough. This is answered by comparing what you have with the cost: $10.00 is enough for a $7.50 item because it is more; $5.00 is not enough for something costing $6.20 because it is less. Often a quick estimate settles it without an exact sum — rounding the prices up and checking they still fit. Deciding whether money is enough is one of the most useful everyday calculations, and it rests on comparing amounts, the same place-value comparison used to order decimals.
Is it enough?
To check if money is enough, compare what you have with the cost.
You have $10.00 and the item costs $7.50. Is that enough?
Money problems all together
Pulling the unit together, real money problems combine all of these: adding prices to a total, working out change, estimating by rounding, multiplying repeated costs and checking whether an amount is enough. A shopping list totalled — $1.20 plus $2.50 plus $1.80 makes $5.50 — is decimal addition in its most everyday form. With money seen as decimals, change found by subtracting, totals estimated by rounding, repeated costs multiplied and amounts compared, a child can handle the money calculations of daily life, the practical pay-off of all the number work of Year 4.
A shopping total
A shopping list is totalled by adding all the prices together.
A shopping list adds up to a total. Reveal each price, then the total.
Quick self-check
1. What is $2.50 + $1.30?
2. You pay $5.00 for something costing $3.60. Your change is...
3. Rounded to the nearest dollar, $4.99 is about...
4. Three apples cost $1.20 each. Altogether they cost...
5. You have $10.00 and want to buy something for $7.50. Do you have enough?