Multiplying Decimals
Multiply ignoring the points, then place the point using total decimal places.
Key idea
Multiply ignoring the points, then place the point using total decimal places.
In depth
Ignore the points, multiply as whole numbers, then place the point so the answer has as many decimal places as both factors combined. This works because each decimal is a whole number divided by a power of 10.
Worked example
0.3 × 0.04: 3 × 4 = 12, three decimal places in total, so 0.012.
Real-world uses
- Calculating the cost of 2.5 kg at £3.40 per kg
- Scaling measurements in science experiments
Common mistake
Lining up decimal points as in addition. That is not needed for multiplication.
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 Multiplying Decimals?
Multiply ignoring the points, then place the point using total decimal places. It is a topic at the intermediate level in Arithmetic & Number Sense.
Where is Multiplying Decimals used in real life?
Real-world examples: Calculating the cost of 2.5 kg at £3.40 per kg; Scaling measurements in science experiments.
What should I learn before Multiplying Decimals?
Make sure you are comfortable with Adding and Subtracting Decimals, the previous topic in Arithmetic & Number Sense.
What is a common mistake with Multiplying Decimals?
Lining up decimal points as in addition. That is not needed for multiplication.
How can I practise Multiplying 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 Multiplying Decimals?
Move on to Dividing 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.