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Expressions using Letter-Numbers

Putting a number in

2n + 3 is written on a bus ticket. It is not an answer yet. Choose a number for n.

2n + 3 — waiting for a value.
Step 1 of 4
  1. 2n + 3 — waiting for a value.
  2. n = 4: 2 × 4 + 3.
  3. 8 + 3.
  4. 11.

Rule: substitution means swapping the letter for its value. Then calculate: multiply first, then add. 2n means 2 × n. Multiplication is done before addition.

Try n = 0: 2 × 0 + 3 = 0 + 3 = 3. Try n = 10: 2 × 10 + 3 = 20 + 3 = 23. One expression, many answers.

Tap the value of each line in the lab. Then read the working, stage by stage.

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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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