Year 5 - Maths
Explain how to identify a prime number or a composite number
Understand and use the concept of factorisation (square and prime numbers)
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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 understand and use the concept of factorisation, explaining what a factor is and how to use arrays and multiplication/division facts to find them. They will identify prime numbers, square numbers and composite numbers.
Lesson Summary
You will learn to explain how to identify a prime number or a composite number.
Key Notes
- A prime number has only 2 factors, 1 and itself.
- A composite number is a number with more than 2 factors.
Vocabulary To Learn
- factor: A factor is a whole number which exactly divides another whole number.
- prime number: A prime number is a whole number greater than one which has exactly two factors.
- composite number: A composite number is a whole number which has more than two factors.
- square number: A square number is the result of multiplying an integer (not a fraction) by itself.
Common Mistakes To Avoid
- Every number has one and itself as a factor, so every number is a prime number.
3 Quick Questions (With Answers)
1. Solve this in steps: explain the method from this lesson and why each step matters.
A prime number has only 2 factors, 1 and itself. A composite number is a number with more than 2 factors.
2. Use this key word in a maths sentence and explain it clearly. 'factor'
A factor is a whole number which exactly divides another whole number. Use this word when showing your method, then check your final answer is reasonable.
3. Spot and fix this common maths mistake.
Mistake: Every number has one and itself as a factor, so every number is a prime number. Correction: Ensure pupils explore the different arrangements that numbers can make with tiles in arrays. Point out that the numbers which cannot be arranged in any way except for one row or column are prime numbers.
More Lessons In This Unit
- Explain how to find all the factors of a number systematically Study Guide
- Explain how to identify a prime factor of a number Study Guide
- Explain what a factor is and use arrays and multiplication and division facts to find them Study Guide
- Use a complete list of factors to explain when a number is a square number Study Guide
Browse all guides in the Year 5 Maths guide library.