Adding and Subtracting Decimals for 4th Grade
TL;DR: To add or subtract decimals, line up the decimal points so tenths sit under tenths and hundredths sit under hundredths. Add or subtract just like with whole numbers, then bring the decimal point straight down into the answer.
Key takeaways:
- Line up the decimal points before you add or subtract.
- Add a trailing zero so both numbers have the same number of decimal places.
- Add or subtract column by column from right to left.
- Bring the decimal point straight down into the answer.
- Regroup (carry or borrow) the same way you do with whole numbers.
This lesson covers adding and subtracting decimals for fourth-grade math. Use the examples and practice below to build confidence and skill.
DETAILED EXPLANATION
Add or subtract decimals by aligning the decimal points and then adding or subtracting as with whole numbers. Keep the decimal point in the same place in the answer.
WORKED EXAMPLES WITH STEP BY STEP SOLUTIONS
Example 1
Add 2.4 + 1.87.
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Solutions:
Step 1: Apply the concept from the lesson above.
Step 2: Carry out the operation or reasoning.
Answer: 2.40 + 1.87 = 4.27
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For a Grade 4 workbook that builds decimal operations into a full year of math, Mastering Grade 4 Math walks through decimals, fractions, and mixed numbers with worked examples. For word-problem practice, Mastering Grade 4 Math Word Problems gives you problems with answer keys.
Frequently Asked Questions
How do I add decimals?
Line up the decimal points one above the other. Add zeros to the right so both numbers have the same number of decimal places. Add column by column. Bring the decimal point straight down. \(2.4 + 1.87\) becomes \(2.40 + 1.87 = 4.27\).
Why do I add a zero to the end of a decimal?
So the columns line up. \(2.4\) and \(2.40\) are the same number — adding a trailing zero doesn’t change the value, but it makes column addition straightforward. Without it, you might add the \(7\) hundredths to nothing and lose your place value.
How do I subtract decimals?
Same idea as adding. Line up the decimal points, pad with zeros so both numbers match in decimal places, then subtract column by column. Borrow when needed. \(5.30 – 1.47 = 3.83\).
What if I forget to line up the decimal points?
You’ll add tenths to hundredths and get a wrong answer. \(2.4 + 1.87\) lined up wrong might give \(4.11\) instead of the correct \(4.27\). Always check that the decimal points are stacked vertically before computing.
How is decimal addition different from whole-number addition?
It’s almost the same — you still add column by column and regroup when needed. The only new part is keeping track of the decimal point. Place value still works the same way: tens, ones, tenths, hundredths.
What is regrouping in decimal addition?
Same as in whole numbers — when a column adds to \(10\) or more, you carry the extra into the next column to the left. \(45 + 80 = 125\) cents means \(1\) dollar and \(25\) cents. Decimals work the same way.
What if the numbers have different numbers of decimal places?
Add trailing zeros to the shorter one so both have the same length. \(3.4 + 0.275\): rewrite as \(3.400 + 0.275 = 3.675\). Adding zeros to the end of a decimal doesn’t change its value.
How do I check my work?
Add the difference back to the smaller number. If \(5.30 – 1.47 = 3.83\), then \(3.83 + 1.47 = 5.30\) should match. Or estimate first: \(5.30 – 1.47\) is roughly \(5 – 1 = 4\), and \(3.83\) is close to \(4\). The estimate matches, so the answer looks right.
How do decimals work with money?
Dollars and cents are decimals: \(\$3.45\) means \(3\) dollars and \(45\) hundredths of a dollar. Adding money is just adding decimals: \(\$3.45 + \$2.80 = \$6.25\). Always keep two decimal places for money.
Where can I get more practice?
EffortlessMath has full Grade 4 workbooks and decimal-focused practice with answer keys.
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If a topic on this page feels rusty, these short lessons go deeper:
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