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Finding Common Ground

The primes inside a number

Break 60 into pieces that will not break any more. Breaking a number means writing it as a product. For example, 60 = 6 × 10.

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60 to break down.
Step 1 of 5
  1. 60 to break down.
  2. Peel off 2: 60 → 30.
  3. Peel off 2 again: 30 → 15.
  4. Peel off 3: 15 → 5.
  5. 5 is prime. 60 = 2 × 2 × 3 × 5.

Keep breaking until nothing breaks

60 breaks into 2, 2, 3 and 5. None of them breaks any more.

A prime has exactly two factors: 1 and itself. Keep splitting a number until every piece is prime. Those pieces are its prime factorisation.

Multiply the pieces together to check. 2 × 2 = 4, then 4 × 3 = 12, then 12 × 5 = 60.

The number 1 has only one factor. So it is not prime. It never appears on the list.

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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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