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Expressions using Letter-Numbers

Putting two expressions together

Two classes bring books to a stall. One brings 3n + 4 crates. The other brings 2n + 5. Can the two amounts be written as one expression?

Write every term in one row: 3n, 4, 2n, 5.
Step 1 of 4
  1. Write every term in one row: 3n, 4, 2n, 5.
  2. Collect the n-terms: 5n.
  3. Collect the plain numbers: 9.
  4. Total = 5n + 9.

Yes. Together they bring 5n + 9 crates.

Rule: add two expressions by writing every term in one row. Then collect like terms.

Taking away is harder. A bracket is the ( ) round some terms. The minus takes away every term inside the bracket. So (5n + 3) − (2n + 1) is 5n + 3 − 2n − 1. That collects to 3n + 2.

Pick a job. Slide n. Compare the long form with the tidy form.

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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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