fractions g. donald allen department of mathematics texas a&m university
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Fractions
G. Donald Allen
Department of Mathematics
Texas A&M University
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From the NCTM…
Middle school should acquire a deep understanding of fractions and be able to use them competently in problem solving.
NCTM(2000)
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From the NAEP…
Reports show that fractions are "exceedingly difficult for children to master. "
Students are frequently unable to remember prior experiences about fractions covered in lower grade levels
NAEP, 2001National Assessment of Educational Progress
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Mathematics Proficiency
Conceptual understanding Procedural fluency Strategic competence Adaptive reasoning Productive disposition
Adding it Up, - National Research Council
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Bottlenecks in K-8
It is widely recognized that there are at least two major bottlenecks in the mathematics education of grades K–8: The teaching of fractionsThe introduction of algebra
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Student mistakes with fractions
Algorithmically based mistakes Intuitively based mistakes Mistakes based on formal knowledge.
e.g. Children may try to apply ideas they have about whole numbers to rational numbers and run into troubleTirosh (2000)
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Polyvalence, again
When it comes to fractions there are multiple interpretations.
What are they? What do students think they are?
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Multiple meanings1. Parts of a whole: when an object is equally divided
into d parts, then a/b denotes a of those b parts.
2. The size of a portion when an object of size a is divided into b equal portions.
3. The quotient of the integer a divided by b.
4. The ratio of a to b.
5. An operator: an instruction that carries out a process, such as “4/5 of”.
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Definition of a fraction
A rational number expressed in the form
a/b --- in-line notation, or
--- traditional "display" notation
where a and b are integers.
ab
This is simply the division of integers by integers.
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Fractions – Basic Syllabus
Basic Fractions Equivalent Fractions Adding Fractions Subtracting Fractions Multiplying Fractions Dividing Fractions
Comparing Fractions Converting Fractions Reducing Fractions Relationships Subtracting Fractions
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Comparing Fractions
Equivalent Fractions Comparing - Like Denominators Comparing - Unlike Denominators Comparing – Unlike numerators and
denominators Comparing Fractions and Decimals
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Converting Fractions
Converting to Mixed Numbers Converting from Mixed Numbers Converting to Percents Converting from Percents Converting to Decimals Converting to Scientific Notation Converting from Scientific Notation
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Reducing Fractions
Prime and Composite Numbers Factors Greatest Common Factor Least Common Denominator Least Common Multiple Simplifying
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Relationships
Relating Fractions To Decimals Relating Decimals to Fractions Relating mixed fractions to improper
fractions Relating improper fractions to mixed
fractions.
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Equivalent fractions
Two fractions are equivalent if they represent the same number.
This means that if then The common factor k has many names.
ab
kakb
ab
cd
cd
kakb
This principle is the single most important fact about fractions.
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Equivalent fractions
Why is
It’s just arithmetic!
a cb c a
b
a cb c 1c c a
b 1 a
b a
b
?
Productive disposition
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Why are equivalent fractions important? For comparing fractions For adding fractions For subtracting fractions For resolving proportion problems For scaling problems For calculus and beyond
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Addition
Addition Addition - Like Denominators Addition - Unlike Denominators Addition Mixed Numbers
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Addition - Like Denominators
Why is
It is by Pie charts? Fraction bars? Spinners? Blocks/Tiles?
ad
bd
a bd
?
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Addition - Like Denominators
Answer. It’s just arithmetic! We know…
So,
d a bd
a b
a bd
1da b a
d b
d
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Common mistakes
Where??? College
ab
ac a
b cab
cd
a cb d
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How to add fractions, #1
Definition of addition. In some sources we see… a
b cd
pa qbm
where m lcmb,d
and m pb qd
What’s wrong with this??
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How to add fractions, #2
Definition of addition. In other sources we see… a
b cd
ab
dd
cd
bb
a db d c b
d b a d c b
b d
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Example – no lcm
12
25 1
2 55 1
2 22
1 52 5 2 2
5 2 1 5 2 2
2 5 910
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Example – with lcm
38
14
38
11
14
22
3 18 1 1 2
4 2 3 1 1 2
8
58
lcm = 8
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Go with the flow
Flow charting a process can reveal unnoticed complexities.
The difference between using the lcm and simple denominator multiplication is not insignificant.
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Add two fractions
Add the equivalent
fractionsReduce
Find the product of the
denominators
Create equivalent fractions
Basic add fractions process
Adding fractions process, #1
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Adding fractions process, #2
Add two fractions
Add the equivalent
fractionsReduce
Find the LCM of denominators
Create equivalent fractions
Advanced add fractions process
A division step here to use the lcm
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Is this too difficult?
Remember this can be regarded as strictly a skill.
It will always be used as a skill – when it is used.
At what point – we may ask – is fundamental understanding suppose to kick in?
Consider calculus – the accepted wisdom
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Is this true?
Informal surveys among teachers consistently reveal that many of their students simply give up learning fractions at the point of the introduction of addition.
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Tips for teaching fractions
Engage your students’ interest in fractions. Stress the importance of fractions in the
world around them and in successful careers.
Emphasize that fractions are used in a variety of ways.
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Tips for teaching fractions
Practice understanding of fractions by using math manipulatives.
Practice basic words or phrases by giving students a problem and a list of relevant terms, e.g., "numerator," "denominator,“
Practice fractions by having students observe their surroundings, e.g., what fraction of classmates have black hair, have brown eyes.
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Tips for teaching fractions
Practice fraction problems by having students write their own fractions based on their own experiences.
Practice fraction problems by having students work in small groups to create their own surveys around fractions based on classmates' preferences
http://www.meritsoftware.com/teaching_tips/tips_mathematics.html#3
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Engaging students…
Pallotta, J. (1999). The hershey's milk chocolate bar fractions. Cartwheel Books.
Adler, D. A., & Tobin, N. Fraction fun. Ginsburg, M. Gator Pie. Leedy, L. Fraction Action. Mathews, L. Gator Pie.
Mostly elementary
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Dividing Fractions
Division Division by Integers
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Multiplying Fractions
Multiplication Multiplication by Integers
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Division of fractions
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Mixed fractions
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Multiplication of fractions