Skip to content
Exit presentation

Expressions using Letter-Numbers

Start here

Tiles are placed in a plus shape that grows each step. Can you find step 40 without building steps 1 to 39?

4n + 1 answers step 40 without building the 39 steps before it.

This is Part I, Chapter 4, Expressions using Letter-Numbers.

What you will learn

A letter-number is a letter that stands for a number.

  • A letter for a number. n holds a number, not yet chosen.
  • A rule in letters. One line answers every step.
  • What 3n means. The times sign is dropped, nothing else.
  • Putting a number in. Swap the letter for a value.
  • Always, or only sometimes. One match is not proof.
  • Terms of the same kind. Terms are parts of an expression. Sort by letter part.
  • Adding whole expressions. Write all terms in one row. Join the like ones.
  • From a situation. A fare or a bill, in one line.
  • A formula. A rule in letters, like a polygon's perimeter.
  • Letters in a calendar. One letter names every date in a square.
  • Spot the slip. Find a small mistake by putting a number in.

Every teaching lesson has a lab. Set a number. Watch the line answer.

Unsure about patterns or the rectangle rule? Open those lessons first.

Jump to lesson

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

Other tracks