Adding and Subtracting Decimals
Line up decimal points, then add or subtract as with whole numbers.
Key idea
Line up decimal points, then add or subtract as with whole numbers.
In depth
Line up the decimal points so equal places sit in the same column, filling gaps with zeros. Then add or subtract as with whole numbers and bring the point straight down.
Worked example
3.5 + 0.28 = 3.50 + 0.28 = 3.78.
Real-world uses
- Totalling bills with pence
- Calculating remaining battery or fuel to the decimal place
Common mistake
Aligning by the right edge instead of the decimal point.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Adding and Subtracting Decimals?
Line up decimal points, then add or subtract as with whole numbers. It is a topic at the intermediate level in Arithmetic & Number Sense.
Where is Adding and Subtracting Decimals used in real life?
Real-world examples: Totalling bills with pence; Calculating remaining battery or fuel to the decimal place.
What should I learn before Adding and Subtracting Decimals?
Make sure you are comfortable with Comparing and Ordering Decimals, the previous topic in Arithmetic & Number Sense.
What is a common mistake with Adding and Subtracting Decimals?
Aligning by the right edge instead of the decimal point.
How can I practise Adding and Subtracting Decimals?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Adding and Subtracting Decimals?
Move on to Multiplying Decimals next.
Related intermediate topics in Arithmetic & Number Sense
- Long Multiplication – Multiply by each digit of the multiplier, shift by place value, then add partial products.
- Long Division – Divide, multiply, subtract and bring down repeatedly to get the quotient.
- Factors and Multiples – Factors divide a number exactly; multiples are its products with whole numbers.
- Divisibility Rules – Quick tests: by 2 last digit even, by 3 digit-sum divisible by 3, by 5 ends 0/5, by 9 digit-sum divisible by 9.
- Prime Numbers – A prime has exactly two positive divisors: 1 and itself.
- Composite Numbers – Numbers greater than 1 with more than two factors.