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Working with Fractions

Taking one fraction from another

You have 3/4 of a ribbon roll. You cut away 1/6 for a border. How much is left?

A strip cut into twelfths.
Step 1 of 4
  1. A strip cut into twelfths.
  2. 3/4 renamed is 9/12.
  3. Take away 1/6, renamed as 2/12.
  4. Left over: 9/12 − 2/12 = 7/12.

Rename, then take away

7/12 of the roll is left.

Rename both fractions onto one shared bottom number. Subtract the top numbers. Keep that bottom number.

Steps of 4 and steps of 6 both reach 12. 12 is 3 steps of 4, so 3/4 is 9/12. 12 is 2 steps of 6, so 1/6 is 2/12. Then 9 − 2 = 7. The roll has 7/12 left.

Sometimes there is not enough to take away. You cannot take 1/2 from 1/3. 1/2 is more than 1/3.

Slide to cross out pieces in the lab. Stop when the crossed-out part matches the fraction taken away.

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This track

  1. 0 Start here
  2. 1 More than one whole
  3. 2 Renaming until the pieces match
  4. 3 Adding pieces that do not match
  5. 4 Taking one fraction from another
  6. 5 Wholes and parts together
  7. 6 Checkpoint: renaming, adding and taking away
  8. 7 A fraction of a whole number
  9. 8 A fraction of a fraction
  10. 9 When multiplying makes it smaller
  11. 10 The number that undoes a fraction
  12. 11 How many of these fit inside that
  13. 12 Checkpoint: multiplying and dividing
  14. 13 Cancel before you multiply
  15. 14 Share a fraction equally
  16. 15 When dividing makes it bigger
  17. 16 A fraction of what is left
  18. 17 The big picture
  19. 18 Track quiz

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