Year 5 - Maths
Multiply 1-digit numbers by decimals
Calculating with decimal fractions
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This pupil-friendly study guide includes a unit summary, clear notes, common mistakes, and quick questions with answers.
Unit Summary
In this unit pupils will explain the effect of multiplying and dividing a number by 10, 100 and 1,000 and use their knowledge of multiplying decimal fractions by whole numbers to solve measures problems.
Lesson Summary
You will learn to explain how to use multiplying and dividing by 10 or 100 to multiply 1-digit numbers by decimal fractions.
Key Notes
- Use place value to convert the decimal fraction by multiplication to a whole number.
- Use unitising, known facts and/or the distributive law to multiply the whole numbers.
- Use place value to convert the number by division to adjust the product.
Vocabulary To Learn
- Unitising: Treating groups that contain the same number of things as 'ones' or 'units'. It is important particularly in handling money and in understanding place value and supports us to think multiplicatively.
- Distributive law: The distributive law says that multiplying a number by a group of numbers added together is the same as doing each multiplication separately.
Common Mistakes To Avoid
- Children may scale the decimal fraction inaccurately or may forget to scale the product accordingly to solve the original equation.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
Use place value to convert the decimal fraction by multiplication to a whole number. Use unitising, known facts and/or the distributive law to multiply the whole numbers.
2. Use this key word in a maths sentence and explain it clearly. 'Unitising'
Treating groups that contain the same number of things as 'ones' or 'units'. It is important particularly in handling money and in understanding place value and supports us to think multiplicatively. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Children may scale the decimal fraction inaccurately or may forget to scale the product accordingly to solve the original equation. Correction: If a decimal fraction has only tenths, we multiply by 10 to form a whole number. If the decimal fraction has hundredths, we multiply by 100 to form a whole number. Remember to adjust the product to answer the original equation.
More Lessons In This Unit
- Converting units of length Study Guide
- Converting units of mass and capacity Study Guide
- Divide decimal fractions by 1-digit numbers Study Guide
- Divide decimal fractions by 1-digit numbers using written methods Study Guide
- Explain how to multiply and divide a number by 10, 100 and 1,000 Study Guide
- Multiply 1-digit numbers by decimal fractions using written methods Study Guide
- Multiply hundredths by whole numbers Study Guide
- Multiply tenths by whole numbers Study Guide
- Multiplying and dividing a number by 10, 100 and 1,000 Study Guide
- Multiplying and dividing a number by 10, 100 and 1,000 including bridging 1 Study Guide
- Predicting the size of a product Study Guide
- Solve measures problems using knowledge of multiplying decimal fractions Study Guide
- The relationship between multiplying by 0.01 and dividing by 100 Study Guide
- The relationship between multiplying by 0.1 and dividing by 10 Study Guide
Browse all guides in the Year 5 Maths guide library.