Finding the highest common factor and lowest common multiple by prime factorisation and by division, the product relation HCF × LCM = product of two numbers, HCF and LCM of fractions, and the standard applications — tolling bells, tiling, and the largest measuring unit.
Reading the 10 sections above, the worked examples and the practice set is free — the whole knowledge base is on the free plan, along with flashcards, private notes and Ask Onely.