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Exit presentation

Finding Common Ground

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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.

6 m pieces use up both rolls, with nothing left over.

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.

Jump to lesson

This track

  1. 0 Start here
  2. 1 The primes inside a number
  3. 2 A factor tree, and where it ends
  4. 3 The biggest one they share
  5. 4 Reading it off the two prime lists
  6. 5 When two step counts meet
  7. 6 The same two lists, read the other way
  8. 7 Which one does the question want?
  9. 8 Check it before you hand it in
  10. 9 Co-prime numbers
  11. 10 One table for the HCF and the LCM
  12. 11 The HCF, the LCM and the product
  13. 12 Checkpoint
  14. 13 The big picture
  15. 14 Track quiz

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