Author note — to cover

HCF of two numbers beyond 100 from index-form prime factorisations, taking each shared prime to its lower index; what HCF means; listing method as backup for small numbers. LCM is the sibling page; three numbers and Venn diagrams live on hcf-lcm-venn. Both tiers. (N4)

Introduction

—coming soon—

Practice and continue

Practice

Highest common factor

Taking each shared prime to the lower index, and what the HCF means.

Next lesson

Lowest common multiple

Every prime to the higher index, and why the LCM is not always the product.