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5. Equivalent Fractions
Answer the following questions:
- what is the difference between six eighths and three quarters?
- what is the difference between two quarters and one half of a dollar?
- what is the difference between two quarters and one half of a length, of
a weight (or mass), and of an hour?
This lesson introduces and provides motivation for equivalent
fractions.
Example:
|
Three Quarters |
3
4 |
|
| Each box is a quarter |
1
4 |
1
4 |
1
4 |
1
4 |
| Each box is a half of a quarter |
|
|
|
|
|
|
|
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Each quarter is two eighths.. Hence 3 quarters is 6 = 3×2 eighths.
Hence
The foregoing equation may be read forwards or backwards. The
fractions
3 and 6
4 8
are equivalent.
Numerals and Fractionals
Numerals: Whole numbers may be written in different ways:
XXII = two tens and three = 2 × 10 + 3 = 23
Thus there are different expressions (numerals) for each and every whole
number.
Fractionals: In the English language, a fraction refers to a part
of a whole. There may be different ways (fractionals) to describe the same
fraction.
Some parts, fractions or fractionals, are given exactly by (A) a
half, a third, a quarter, a fifth, a sixth, a seventh or a unit
numerator fractions; and some further fractions are given exactly by
whole number multiples of unit numerator fractions, for example two
thirds, two quarters, three quarters, two fifths, three fifths, four
fifths, two sixths, three sixths, four sixths, five sixths and so on.
Consider an example.
|
1 |
|
1
3 |
1
3 |
1
3 |
|
_1_
12 |
_1_
12 |
_1_
12 |
_1_
12 |
|
|
|
|
_1_
12 |
_1_
12 |
_1_
12 |
_1_
12 |
Let us go over that again.
In the diagram, we see a single third can be divided into four parts of
equal size and value. Each of those parts is a twelfth and equals a
fourth of a third. Four quarters of a divisible object is the
object. So one third is four times a quarter of itself. That
is
Whence two thirds would be twice as much:
Thus different fractions
|
1 |
2
3 |
1
3 |
|
1
3 |
1
3 |
1
3 |
|
_1_
12 |
_1_
12 |
_1_
12 |
_1_
12 |
|
|
|
|
_1_
12 |
_1_
12 |
_1_
12 |
_1_
12 |
Here the same part of the length, namely 2 thirds may be described in
two different ways
Thus different fractionals may describe the same part or fraction of a
whole. When they do, the fractional are said to be equivalent. That
is, they have the same value.
Note: Same value and same meaning are slightly
different. The fraction 2 thirds and 8 twelfths have the same
value for many purposes. Taking two thirds of a cake (literally dividing
it into thirds and taking two of those thirds) and taking 8 twelfths of
a cake, the same cake, may physically represent different
operations.
Extension: In the above diagram, we see a single length 1 can be
divided into three parts of equal size and value. Each of those
parts is a third. Three thirds has the same size as one.
Thus
Thus 1 has the same value as the fraction 3 thirds. Thus a single
fractional may be also be a numeral, that is a different way to express a
whole number, here the number one.
Note Again: Same value and same meaning are slightly
different. The fraction 3 thirds and the number one have the
same value for many purposes. But three thirds of a apple (literally
dividing it into thirds and taking all three of those thirds) and
taking a whole apple are different. A whole apple with its
skin intact will last longer than three thirds, each with the interior
of the apple exposed to the air.
|
Algebraic Shorthand Description of ideas
for reading as part of algebra skill development -
optional reading for now
- Assume N = 4 and M = 5 and B = 3 on first reading
below.
We may use the property of divisible objects (fractions included)
| N |
× ( |
1
N |
of an object
|
)
|
= the object
|
Thus if we have a fraction
B
M
of an object then
| N |
× ( |
1
N |
of
|
B
M
|
of an object |
) = |
B
M
|
of the object |
In shorthand we see
or equivalently
The latter in turn gives the common factor cancellation property
The left and right hand side in foregoing equation are said to be equivalent
fractions. Replacing the left hand side by the right hand side in a
calculation is called a simplification, a reduction, a cancellation or a
lowering of terms. On the other hand, replacing the right hand side by the
left hand side is called raising terms. Raising of terms is useful in the
addition and multiplication of fractions.
In the computation of fractions, we may also use
View the following RealPlayer videos after this lesson
- [Play
Video] 3-4 minutes. Equivalent
fractions - Lowering and raising terms
(the values of numerators and denominators) to
obtain equivalent fractions. Simplification
involves lowering terms - cancelling common
factors or divisors on top and bottom.
Addition & subtraction of fractions may
involve raising terms to obtain a common
denominators. See below.
- [Play
Video] 2-3 minutes A few examples of
Simplifying Fractions - lowering terms by
canceling common factors until there are no
more common factors, so that the numerator and
denominator are relatively prime, that is
there prime decompositions have no primes in
common.
Question (involving fractions of a set)
- Tom see one hundred pennies. He takes a tenth of them. Jane takes a
ninth of what remains. Then Andrew takes an eight of what is left after
Janes pick. Jean takes a tenth of the rest? Finally, Tom takes two
ninths of the what remains? Who has the least number of pennies?
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Four Topics
Section Entrance Fraction Guide Fractions with Units Guide Ratios & Fractions Guide Proportionality Guide Links
Fraction How-TOs 1 What is a Fraction 2 Fraction Multiplication I 3 Fraction Multiplication II 4 Fraction Multiplication III 5 Equivalent Fractions 6 - Products Algebraically 7. Mixed Numbers Etc., 8. Fraction Comparison, Etc 9 Fraction Addition I 10. Fraction Addition II 11. Add, Subtract or Compare 12. Fraction Addition III 13 Fraction Multiplication IV 14. Fraction Division & Reciprocals 15. Division Formulas Justified 16. Rational Numbers 17. Fraction Webvideos 18 Geometric Notes
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For
Senior
High School & Calculus Students
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<| (o) (o)
|>
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/
\___ _/
||
-/[]\-
||
/ \_
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Words to clearly
introduce algebra and variables
have been missing in course design. For people who cannot do
algebra,
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the missing words may
explain or ease their difficulties. Volume 2 ,Three
Skills for Algebra, in Chapters
8 to 14 & 18 etc, puts words before symbols to
providing the missing words in a way that enrich the
comprehension of all. Those words form the middle part of a algebra
(and logic) lessons aimed at helping or improving all
of high school mathematics and also calculus course
design & delivery.
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For Avid Readers in School & Out -
Online Books
1. Elements of
Reason. 1996
1A. Pattern
Based Reason 1995
1B. Math
Curriculum Notes 1996
2. Three
Skills for Algebra 1995
3.Why
Slopes & More.Math
1995
Tour their forewords.
Calculus Prep or Help: See Volumes 2 & 3,
and this bigger
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For Parents: Speaking
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skill development booklets for ages 4-14.
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Mostly
For High
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Intro to Solving
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school students. Question for Tutors: When do
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here?
Fraction
Skills, thought-based development, Ages 10 to 14 may need a
tutor. Students who have to understand in order
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For Senior
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4 curious Algebra
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Words before & besides symbols. A Key Algebra
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Preview (1st intro)
Four Calculus
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Intro to Complex
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These lessons introduce skills differently Would you
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More Topics
1. Decimal
Arithmetic Reference!
2. Integers
- Intro to Signed No.s
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- fully explained.
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with Units
5. Number
Theory,
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7 Formulas
for- & backwards -
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9. Logic
Chapters:
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11. Slopes
& Equations of Straight Lines. (Take
I. See take II below)
12. Why
Study Slopes.
13. Maps,
Plans, Similarity & Trig,
(Take II included here)
14. Quadratics:
Starter lessons
15. Polynomials:
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16 Why
Factor Polynomials:
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19. Complex
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Circuits Etc
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22. The
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Level I Material: New Stuff
Time and Date Matters
Level I Arithmetic.
Money Matters
Measurement Matters
Matters of Chance (Risk Control)
Logic
Chapters
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Using/Making Maps and Plans.
(A variant of
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Plans, Similarity & Trig, to
appear here).
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-
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Essays
(opinions,
possibilities, references)
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will be given in online meeting place with voice &
whiteboard.
- Math & Logic How-TOs
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5. More Geometry
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7. Show Work or Logic
These may be too dense for students. Offering ideas to change
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