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Proper fractions

Proper fractions. The value of the numerator is less than the value of the denominator. Proper in this case does not mean correct or best. Improper fractions. The value of the numerator is greater than or equal to the value of the denominator. What do we mean by the term unit fraction?.

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Proper fractions

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  1. Proper fractions The value of the numerator is less than the value of the denominator. Proper in this case does not mean correct or best.

  2. Improper fractions The value of the numerator is greater than or equal to the value of the denominator.

  3. What do we mean by the term unit fraction?

  4. Unit Fractions Unit fractions are fractions whose numerator is 1: 1 1 1 1 1 2 7 24 100 8

  5. Operations with fractions • Addition • Subtraction • Multiplication • Division

  6. Adding and subtracting fractions

  7. 1/2 + 1/3

  8. Mixed numbers • Meaning of

  9. Writing mixed numbers as improper fractions The algorithm that is taught in schools obscures the meaning. This is true for many algorithms, which are “efficient” ways of carrying out operations.

  10. Write mixed number as improper fraction and vice versa

  11. Multiplying fractions • Repeated addition model • Area model

  12. Multiplication of fractions • Fraction as operator • The multiplication algorithm is best explained by the area model.

  13. Use an area model to multiply1/2 by 5/7

  14. Multiply 2 1/3 by 1 5/6

  15. Dividing fractions • Division of fractions is most easily understood as repeated subtraction.

  16. 12 ÷ ½

  17. 11 divided by 1 1/2

  18. Multiplicative Inverses • We know that division is the inverse of multiplication.

  19. Multiplicative inverses • The multiplicative inverse of a is 1/a • The multiplicative inverse of a/b is b/a

  20. Dividing fractions Because division is the inverse operation of multiplication, dividing a number by a fraction is equivalent to multiplying the number by the multiplicative inverse, called the reciprocal, of the fraction.

  21. Exploration 5.12 • “Drawn to scale” • Part 1 Use reasoning not algorithms to answer #1 • Part 2 Write justifications for the following: • #1: 3, 6, 8, 13, 16 • #2: 1, 2, 7, 8, 9, 13, 15, 16

  22. Worksheet: Dividing Fractions

  23. Problems

  24. Extra Practice • 1. You have from 10:00 - 11:30 to do a project. At 11, what fraction of time remains? At 11:20, what fraction of time remains? • Use a diagram to explain how you know. Are there certain diagrams that are more effective? Discuss this with your group.

  25. Extra Practice • 2. Is 10/13 closer to 1/2 or 1? • Use a diagram to explain how you know. Are there certain diagrams that are more effective? Discuss this with your group.

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