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Two ribbons, 12 m and 18 m. Cut both into equal pieces. Nothing is left over.

6 goes into 12, because 12 ÷ 6 = 2 with nothing left over. It goes into 18 too, because 18 ÷ 6 = 3.

Your textbook calls this Part II, Chapter 3, Finding Common Ground.

What you will learn

• Primes inside — break any number into primes.
• A factor tree — split it any way. The end primes stay the same.
• The HCF — the highest common factor. It is the biggest number that goes into both.
• The LCM — the lowest common multiple. It is the smallest number that both go into.
• Which one — read what the answer must do.
• Check it — two tests find a wrong answer.
• Co-prime — two numbers that share only the factor 1.
• One table — divide both numbers together. Read the HCF and the LCM from it.
• The product rule — HCF times LCM equals the two numbers multiplied.

Every lesson has a small lab. Tap it and see the idea work.