Adding and Subtracting Decimals

What You Will Learn

• Line up decimal points before calculating.
• Add decimals with different numbers of decimal places.
• Subtract decimals accurately, including regrouping.
• Use zeros as placeholders when helpful.
• Solve money, distance and measurement problems.

1. The Golden Rule: Line Up Decimal Points

When adding or subtracting decimals, digits with the same place value must be in the same column. Ones go under ones, tenths under tenths, and hundredths under hundredths.

You can add zeros to the end of a decimal to make the numbers easier to line up. For example, 3.7 = 3.70.

2. Add Decimals

Worked example: 4.35 + 2.8

1. Write 2.8 as 2.80 so both numbers have two decimal places.
2. Line up the decimal points.
3. Add from right to left: hundredths, tenths, ones and then tens if needed.
4. Keep the decimal point in line in the answer.

Answer: 7.15.

Another example: 0.76 + 0.19

Hundredths: 6 + 9 = 15. Write 5 and carry 1. Tenths: 7 + 1 + 1 = 9. The answer is 0.95.

3. Subtract Decimals

Worked example: 5.2 − 1.76

1. Write 5.2 as 5.20.
2. Line up the decimal points.
3. Subtract from right to left. Regroup from the ones column when needed.
4. Keep the decimal point in line.

Answer: 3.44.

Check by addition: 3.44 + 1.76 = 5.20. This confirms the subtraction.

4. Understand Regrouping

Sometimes you cannot subtract a digit because the top digit is smaller. Regroup one unit from the place to its left. Remember that one tenth equals ten hundredths, and one whole equals ten tenths.

5. Estimate to Check Your Answer

Before or after calculating, round the numbers to easy values. Your exact answer should be reasonably close to the estimate.

Estimation can help you notice a misplaced decimal point or an arithmetic mistake.

6. Solve Everyday Problems

Example 1: Shopping

A notebook costs $2.45 and a pen costs $1.30. What is the total cost?

$2.45 + $1.30 = $3.75.

Example 2: Distance

A runner travels 4.8 km in the morning and 2.65 km in the evening. How far does the runner travel altogether?

4.80 + 2.65 = 7.45 km.

Example 3: Remaining water

A jug contains 3.5 litres of water. A family uses 1.75 litres. How much remains?

3.50 − 1.75 = 1.75 litres.

7. Common Mistakes to Avoid

8. Practice Exercises

Try these before revealing the answers.

1. 2.4 + 1.35
2. 6.78 + 0.9
3. 9.5 − 3.25
4. 7.02 − 1.8
5. 0.86 + 0.47
6. 10 − 4.65
7. A book costs $4.75 and a ruler costs $1.20. What is the total?
8. A bottle contains 2.5 litres. If 0.85 litre is poured out, how much remains?

9. Test Your Understanding

Choose one answer for each question, then select Check Answers. Each question is worth one point.

10. Free Printable Worksheet

Print this worksheet or save it as a PDF for extra practice.

11. Lesson Summary

• Line up decimal points before adding or subtracting.
• Use zeros as placeholders to make place values clear.
• Add or subtract from right to left, regrouping when needed.
• Keep the decimal point aligned in the answer.
• Estimate to check whether your answer is reasonable.