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Finding the Unknown

A bracket in the equation

Four gift bags are packed alike. Each has some sweets and 3 chocolates. The four bags hold 44 things. Let s be the sweets in one bag. A bracket, as in 4(s + 3), groups what one bag holds. How many sweets are in one bag?

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Four bags, each s + 3: 4(s + 3) = 44.
Step 1 of 5
  1. Four bags, each s + 3: 4(s + 3) = 44.
  2. Way 1: share both sides by 4. Each bag holds 11.
  3. Take 3 off both sides: s = 8.
  4. Way 2: multiply 4 into each part of the bracket.
  5. Take 12 off both sides, then share by 4: s = 8.

Two ways to work with a bracket

4(s + 3) means four bags. The bracket (s + 3) is one bag. Each bag has s sweets and 3 chocolates.

In Way 1, share both sides by 4. That gives s + 3 = 11, because 44 ÷ 4 = 11. Take 3 off both sides: s = 8, because 11 − 3 = 8.

In Way 2, count the sweets and the chocolates separately. Four bags hold 4s sweets and 12 chocolates, because 4 × 3 = 12. So 4s + 12 = 44. Take 12 off both sides: 4s = 32, because 44 − 12 = 32. Share by 4: s = 8, because 32 ÷ 4 = 8.

Both ways end at 8. Check in the first line: 4 × (8 + 3) = 44.

Rule: Share both sides by the number outside. It cannot be 0. Or multiply it into every part of the bracket. Either way the answer stays.

Watch out!

Multiply the 4 into s alone and 4s + 3 = 44 is a different line. Put 8 in it: 4 × 8 + 3 is 35, not 44.

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This track

  1. 0 Start here
  2. 1 The equals sign is a balance
  3. 2 One waits, the other claims
  4. 3 Is this the one?
  5. 4 Take it off both sides
  6. 5 Share both sides
  7. 6 Two steps, undone backwards
  8. 7 From a puzzle to a line
  9. 8 Put it back in
  10. 9 The unknown on both sides
  11. 10 A bracket in the equation
  12. 11 When no number fits
  13. 12 Find the first wrong line
  14. 13 Checkpoint
  15. 14 The big picture
  16. 15 Track quiz

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