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Class 6

Chapter 5: Prime Time

A prime number is a number greater than 1 with exactly two factors: 1 and itself. Numbers that are not prime (and greater than 1) are composite. Every composite number can be written as a product of primes — its prime factorisation.

Learning outcomes

  • Identify factors, multiples and primes
  • Apply prime factorisation

Activities

  • Sieve of Eratosthenes hands-on

Worked examples

Read through these first, then try the practice below.

  1. Example 1 — Prime or composite?

    Is 17 prime or composite?

    Solution: The only factors of 17 are 1 and 17. So 17 is prime.

  2. Example 2 — Prime factorisation

    Find the prime factorisation of 30.

    Solution: 30 = 2 × 15 = 2 × 3 × 5. Answer: 2 × 3 × 5.

Self-do practice

Question 1 of 3 · Score 0/0

Which of these is a prime number?

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