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Expressions using Letter-Numbers

Always, or only sometimes

Two shops sell notebooks. Shop A charges 5n rupees for n notebooks. Shop B charges 2n + 3 rupees. For one notebook, both charge ₹5.

n = 1: 5n = 5. 2n + 3 = 5. Match!
Step 1 of 3
  1. n = 1: 5n = 5. 2n + 3 = 5. Match!
  2. n = 2: 5n = 10. 2n + 3 = 7. Apart.
  3. One match is not proof.

Rule: two expressions are the same when they match at every value. One match proves nothing. One mismatch shows they are different.

Both n + n and 2n mean two lots of n. So they match at every value.

Pick a pair. Tap to try n = 1, 2 and on.

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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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