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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.
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Improper fractions The value of the numerator is greater than or equal to the value of the denominator.
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Mixed numbers Meaning of
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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.
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Write mixed number as improper fraction and vice versa
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Operations with fractions Addition Subtraction Multiplication Division
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Adding and subtracting fractions
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1/2 + 1/3
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Multiplying fractions Repeated addition model Area model
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Multiplication of fractions Fraction as operator The multiplication algorithm is best explained by the area model.
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2/3 of 2 1/2
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Mixed number times mixed number
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Dividing fractions Division of fractions is most easily understood as repeated subtraction.
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11 divided by 1 1/2
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Multiplicative Inverses We know that division is the inverse of multiplication.
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Multiplicative inverses The multiplicative inverse of a is 1/a The multiplicative inverse of a/b is b/a
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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.
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Exploration 5.12 “Drawn to scale” Part 1 Use reasoning not algorithms to answer #1 Part 2 Choose a model from the list that was not represented in the problems and make up a story problem using the fraction ¾. Are there any models that are not possible with fractions? Explain.
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Operations with fractions Addition Subtraction
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Operations with fractions Multiplication
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Operations with fractions Division
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Exploration 5.13 Begin in class and finish for homework: 5.13 Part 1: #2-7 Part 2: Choose one of the models from the list that was not illustrated in the problems in Part 1 and write a story problem using the fraction ¾. Also, are there any models that are not possible with fractions? Explain. Homework problems from the textbook: pp. 303-305: 3b,d,e,f, 13, 21, 22, 25 Note that in #3, you should not use algorithms to calculate the result; use reasoning to decide the answer to the question.
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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.
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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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Extra Practice 3.If a/b = 3/4, will the value of (a + x)/(b + x) be less than, equal to, or greater than 3/4. 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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Exploration 5.14 Read the directions carefully and do #1 Discuss with your partner Do #2 Discuss with your partner Do # 3
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Homework for Tuesday Exploration 5.15 Read section 5.3 in your textbook Do problems pp. 305-307: 30, 31, 33, 36, 41, 44a,c,d,h,k, 45a, 48
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