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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. 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?. - PowerPoint PPT Presentation
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Proper fractionsThe 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?
Unit FractionsUnit fractions are fractions whose numerator
is 1:
1 1 1 1 1
2 7 24 100 8
Operations with fractions• Addition
• Subtraction
• Multiplication
• Division
Adding and subtracting fractions
1/2 + 1/3
Mixed numbers• Meaning of
325
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.
Write mixed number as improper fraction and vice versa
312
423
Multiplying fractions
• Repeated addition model
• Area model
Multiplication of fractions
• Fraction as operator
• The multiplication algorithm is best explained by the area model.
Use an area model to multiply1/2 by 5/7
Multiply 2 1/3 by 1 5/6
Dividing fractions• Division of fractions is most easily
understood as repeated subtraction.
212
12 ÷ ½
11 divided by 1 1/2
Multiplicative Inverses• We know that division is the inverse of
multiplication.
52110
5210
Multiplicative inverses• The multiplicative
inverse of a is 1/a
• The multiplicative inverse of a/b is b/a
11
aa
1ab
ba
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.
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
Worksheet: Dividing Fractions
Problems
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.
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.