Add & subtract decimals - Same decimal places
Theory
To add or subtract decimals, line up the decimal points so each place sits in its own column, then work from the right. Carry and regroup just like whole numbers, and bring the point straight down.
To add or subtract decimals, write them one under the other with the decimal points lined up.
Lining up the points keeps ones under ones, tenths under tenths, and hundredths under hundredths.
Work each column from the right, carrying or regrouping exactly as with whole numbers.
Bring the decimal point straight down into the answer.
Working \(4.25 + 3.68\) one column at a time, starting from the hundredths.
| Column | Add | Write | Carry |
|---|---|---|---|
| Hundredths | \(5+8=13\) | \(3\) | \(1\) |
| Tenths | \(2+6+1=9\) | \(9\) | — |
| Ones | \(4+3=7\) | \(7\) | — |
How to add or subtract decimals
- Line up the points. Write the numbers so the decimal points sit in a straight line.
- Work from the right. Add or subtract each column, starting with the smallest place.
- Carry or regroup. Treat the columns just like whole numbers.
- Bring the point down. Place the decimal point straight down into the answer.
Add tenths, then ones.
| \(3.4 + 2.5\) | \(=\) | \(5.9\) |
Tenths \(9+7=16\), carry \(1\).
| \(6.9 + 4.7\) | \(=\) | \(11.6\) |
Regroup the hundredths and tenths.
| \(9.45 - 2.78\) | \(=\) | \(6.67\) |
The change is $7.25.
| \(20.00 - 12.75\) | \(=\) | \(7.25\) |
Common pitfalls
Frequently asked questions
How do you add decimals?
Line up the decimal points, then add each column from the right, carrying when a column reaches ten. Bring the point straight down.
What lines up when adding decimals?
The decimal points. That keeps ones under ones, tenths under tenths and hundredths under hundredths.
Do you carry with decimals?
Yes. If a column of tenths or hundredths reaches ten, write the ones digit and carry \(1\) into the next column, just like whole numbers.
How do you subtract decimals with regrouping?
Line up the points, then borrow from the next column when a top digit is too small. For \(9.45 - 2.78\) you regroup to get \(6.67\).
Where does the decimal point go in the answer?
Straight down, in line with the points above it. This keeps every place in its correct column.