Add & subtract money
Theory
Adding and subtracting money is a Year 3 skill: working with amounts in dollars and cents such as \(\$12.60\). This Year 3 maths page shows how to line up the decimal points, add or subtract the cents and then the dollars, regroup 100 cents as one dollar, and work out change and how much more money is needed. Curriculum: VC2M3N08 / AC9M3N06.
An amount of money has two parts. The dollars come before the decimal point and the cents come after it. In \(\$12.60\) there are 12 dollars and 60 cents. Cents always take two digits, so five dollars is written \(\$5.00\) and \(\$5.05\) means five dollars and five cents.
To add or subtract money, write the amounts one under the other with the decimal points lined up. Work the cents first, then the dollars, just like ordinary numbers. There are 100 cents in one dollar, so \(100\text{c} = \$1\).
Change is the money you hand over take away the price. If a sandwich costs \(\$2.80\) and you pay with a \(\$5\) note, the change is \(\$5.00 - \$2.80 = \$2.20\). You can also count up from the price to the note: \(20\)c makes \(\$3.00\), then \(\$2\) makes \(\$5.00\).
Money does not need formulas, but these facts help you set out and check every money sum.
How to add or subtract money
- Line up the decimal points. Write one amount under the other so cents sit under cents and dollars under dollars. Fill whole dollars with two-digit cents, like \(\$8.00\).
- Work the cents, then the dollars. Add or subtract the cents column first, then the dollars column.
- Regroup and answer. If adding cents reaches 100 or more, carry \(\$1\) to the dollars. Write the answer with a dollar sign and two-digit cents.
How to count up to find change
- Jump to a round number. From the price, jump to the next \(10\)c and then to the next whole dollar.
- Jump to the note. Jump from that whole dollar up to the money paid.
- Add the jumps. The jumps added together are the change. Check: price \(+\) change \(=\) money paid.
| \(\text{cents: }75 + 60\) | \(=\) | \(135\text{c} = \$1.35\) |
| \(\text{dollars: }\$5 + \$2 + \$1\) | \(=\) | \(\$8\) |
| \(\$5.75 + \$2.60\) | \(=\) | \(\$8.35\) |
The total is \(\$8.35\).
| \(\$13.45 \to \$14.00\) | \(=\) | \(55\text{c}\) |
| \(\$14.00 \to \$20.00\) | \(=\) | \(\$6\) |
| \(55\text{c} + \$6\) | \(=\) | \(\$6.55\) |
The change is \(\$6.55\).
| \(\$12.50 \to \$13.00\) | \(=\) | \(50\text{c}\) |
| \(\$13.00 \to \$18.00\) | \(=\) | \(\$5\) |
| \(50\text{c} + \$5\) | \(=\) | \(\$5.50\) |
Ravi needs \(\$5.50\) more.
| \(\$8.90\) | \(\approx\) | \(\$9\) |
| \(\$5.15\) | \(\approx\) | \(\$5\) |
| \(\$9 + \$5\) | \(=\) | \(\$14\) |
The total is about \(\$14\). The exact total is \(\$14.05\).
| \(\$3.40 + \$1.85\) | \(=\) | \(\$5.25\) |
| \(\$5.25 + \$2.50\) | \(=\) | \(\$7.75\) |
| \(\$10.00 - \$7.75\) | \(=\) | \(\$2.25\) |
Her change is \(\$2.25\). That is less than \(\$2.50\), so she cannot also buy the drink.
| \(\$5.35 \to \$5.40\) | \(:\) | \(5\text{c}\) |
| \(\$5.40 \to \$6.00\) | \(:\) | \(60\text{c}\) |
| \(\$6.00 \to \$10.00\) | \(:\) | \(\$4.00\) |
| \(5\text{c} + 60\text{c} + \$4.00\) | \(=\) | \(\$4.65\) |
Ben's change is \(\$4.65\). Check: \(\$5.35 + \$4.65 = \$10.00\).
Common pitfalls
Frequently asked questions
How do you add money with dollars and cents?
Write the amounts one under the other with the decimal points lined up. Add the cents first, then the dollars. If the cents reach 100 or more, regroup \(100\text{c}\) as \(\$1\) and carry it to the dollars column.
How do you work out change from a note?
Change means subtract the price from the money you paid. For a \(\$7.35\) item paid with a \(\$10\) note, count up: \(65\text{c}\) makes \(\$8\), then \(\$2\) makes \(\$10\), so the change is \(\$2.65\).
How many cents are in a dollar?
There are 100 cents in one dollar, so \(100\text{c} = \$1\). When you add cents that reach 100, you regroup them as a dollar.
Why do you line up the decimal points when adding money?
Lining up the decimal points keeps the cents under the cents and the dollars under the dollars. If they are not lined up you might add cents to dollars and get the wrong total.
Is 5 dollars the same as 5 dollars 00 cents?
Yes. Cents always take two digits, so \(\$5\) is written \(\$5.00\) when you set out a money sum. This keeps the columns lined up.
How do you work out how much more money you need?
Subtract the money you have from the price. The difference is how much more you need. For a \(\$15.00\) item with \(\$9.80\) saved, you need \(\$5.20\) more.
How do you work out the change when you buy three things?
Add all the prices first to get the total. Then take the total away from the money you paid. For items costing \(\$3.40\), \(\$1.85\) and \(\$2.50\), the total is \(\$7.75\) and the change from \(\$10\) is \(\$2.25\).