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Expressions using Letter-Numbers

What 3n really means

The tile rule 4n + 1 has no times sign. Here are three ways to write "three lots of n." That means n taken three times.

n + n + n — three lots, spelled out.
Step 1 of 3
  1. n + n + n — three lots, spelled out.
  2. 3 × n — three lots, with a times sign.
  3. 3n — the times sign dropped. Same number.

Rule: a times sign between a number and a letter is dropped. Dropped means not written. 3 × n is written 3n — still three lots of n.

At n = 5, 3n = 3 × 5 = 15. It is not 35. The 3 and the 5 are not two digits of one number.

Pick a value for n. The lab compares 3n with the digits side by side.

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This track

  1. 0 Start here
  2. 1 A letter can hold a number
  3. 2 One rule, written once, for every step
  4. 3 What 3n really means
  5. 4 Putting a number in
  6. 5 Always, or only sometimes
  7. 6 Terms of the same kind
  8. 7 Putting two expressions together
  9. 8 Writing an expression for a real situation
  10. 9 A formula is a rule in letters
  11. 10 Letters in a calendar square
  12. 11 Spot the slip
  13. 12 Checkpoint: formulas, calendars and slips
  14. 13 The big picture
  15. 14 Track quiz

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