AI generatedNumberKS3 / GCSE

Highest common factor from prime factors

Highest common factor from prime factors.

  • Write both numbers as products of primes.
  • The HCF uses only shared primes, each with its smaller power.
  • The LCM uses every prime present, each with its larger power.

Example 1

Find the HCF of 12 and 18 using prime factors.

Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.

Example 2

Find the HCF of 14 and 21 using prime factors.

Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.

Your turn

Question 1

Find the HCF of 16 and 24 using prime factors.

Check answer
Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.
Question 2

Find the HCF of 18 and 27 using prime factors.

Check answer
Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.
Question 3

Find the HCF of 20 and 30 using prime factors.

Check answer
Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.
Question 4

Find the HCF of 22 and 33 using prime factors.

Check answer
Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.
Question 5

Find the HCF of 24 and 36 using prime factors.

Check answer
Write each number as a product of prime factors.For the HCF, take the smaller power of each shared prime.
HCFMultiply the selected prime factors.
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