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Mathematics Class 7

Finding Common Ground

Primes, HCF and LCM, co-prime pairs, one division table, and HCF × LCM.

15 lessons · ~97 min total

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Lessons in this topic

  1. 0 Start here A roadmap: primes inside a number, a factor tree, the biggest shared factor, and the smallest shared multiple. · 4 min You are here
  2. 1 The primes inside a number Every whole number above 1 breaks down into primes, and only one set of them. · 6 min
  3. 2 A factor tree, and where it ends A factor tree splits a number any way you like — the branch ends always come out the same. · 7 min
  4. 3 The biggest one they share Two numbers share several factors, and the largest of those is their highest common factor. · 6 min
  5. 4 Reading it off the two prime lists Pair the two prime lists off, one piece against one piece, and what pairs up multiplies to the HCF. · 7 min
  6. 5 When two step counts meet Two step counts share some numbers, and the first shared number is their lowest common multiple. · 7 min
  7. 6 The same two lists, read the other way Pool the two prime lists, taking the most of each piece, and the pool multiplies to the LCM. · 7 min
  8. 7 Which one does the question want? Ask what the number has to do: go into both numbers, or have both numbers go into it. · 7 min
  9. 8 Check it before you hand it in Two tests each: the HCF must go into both and be beaten by nothing, the LCM must have both go into it and beat everything smaller. · 7 min
  10. 9 Co-prime numbers Two numbers that share only the factor 1 are co-prime. · 6 min
  11. 10 One table for the HCF and the LCM One table of divisions gives both the HCF and the LCM. · 7 min
  12. 11 The HCF, the LCM and the product The HCF times the LCM equals the two numbers multiplied together. · 7 min
  13. 12 Checkpoint Four quick checks before the big picture. · 4 min
  14. 13 The big picture Eleven ideas, tied back together. · 6 min
  15. 14 Track quiz Cheat-sheet table plus a reveal quiz — one question per idea. · 9 min
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