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+ <!DOCTYPE html>
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+ <!-- Cite Beginning and Intermediate Algebra by Tyler Wallace is licensed under a Creative Commons
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+ Attribution 3.0 Unported License. (http://creativecommons.org/licenses/by/3.0/)
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+ Based on a work at http://wallace.ccfaculty.org/book/book.html. pages 12-15-->
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+
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+
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+ < html >
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+ < head >
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+ < title > MAT-101: Module 1A Fractions</ title >
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+ < style >
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+ table , td
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+ {
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+ padding-top : 0.5em ;
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+ padding-bottom : 0.5em ;
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+ }
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+ table .center
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+ {
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+ margin-left : auto;
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+ margin-right : auto;
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+ }
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+ </ style >
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+ < script type ="text/x-mathjax-config ">
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+ MathJax . Hub . Config ( { tex2jax : { inlineMath : [ [ '$' , '$' ] , [ '\\(' , '\\)' ] ] } } ) ;
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+ </ script >
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+ < script type ="text/javascript "
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+ src ="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML ">
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+ </ script >
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+ </ head >
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+
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+ < body >
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+ < b > Fractions</ b > < br > < br >
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+ Working with fractions is a very important foundation to algebra. Here we will
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+ briefly review reducing, multiplying, dividing, adding, and subtracting fractions.
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+ As this is a review, concepts will not be explained in detail as other lessons are.
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+ < br > < br >
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+ < b > World View Note:</ b > The earliest known use of fraction comes from the Middle
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+ Kingdom of Egypt around 2000 BC!
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+ < br > < br >
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+ We always like our final answers when working with fractions to be reduced
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+ (the numerator and denominator are divided by their greatest common factor (GCF)). This is shown in the following example:
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+ < br > < br >
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+
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+ < b > Example 1A-1:</ b > < br >
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+ < center >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{36}{84}$</ td >
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+ < td > Both numerator and denominator are divisible by $4$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{36 \div 4}{84 \div 4} = \dfrac{9}{21}$</ td >
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+ < td > Both numerator and denominator are still divisible by $3$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{9 \div 3}{21 \div 3} = \dfrac{3}{7}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ </ center >
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+ < br >
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+
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+ The previous example could have been done in one step by dividing both numerator
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+ and denominator by $12.$ We also could have divided by $2$ twice and then
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+ divided by $3$ once (in any order). It is not important which method we use as
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+ long as we continue reducing our fraction until it cannot be reduced any further.
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+ < br > < br >
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+ The easiest operation with fractions is multiplication. We can multiply fractions
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+ by multiplying straight across, multiplying numerators together and denominators
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+ together.
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+ < br > < br >
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+
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+ < b > Example 1A-2:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{6}{7} \cdot \dfrac{3}{5}$</ td >
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+ < td > Multiply numerators across and denominators across</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{18}{35}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ When multiplying we can reduce our fractions before we multiply. We can either
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+ reduce vertically with a single fraction, or diagonally with several fractions, as
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+ long as we use one number from the numerator and one number from the denominator.
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+ < br > < br >
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+
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+ < b > Example 1A-3:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{25}{24} \cdot \dfrac{32}{55}$</ td >
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+ < td > Reduce $25$ and $55$ by dividing by $5$. Reduce $32$ and $24$ by dividing by $8$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{5}{3} \cdot \dfrac{4}{11}$</ td >
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+ < td > Multiply numerators across and denominators across</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{20}{33}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ Dividing fractions is very similar to multiplying with one extra step. Dividing
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+ fractions requires us to first take the reciprocal of the second fraction and multiply.
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+ Once we do this, the multiplication problem solves just as the previous
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+ problem.
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+ < br > < br >
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+
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+ < b > Example 1A-4:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{21}{16} \div \dfrac{28}{6}$</ td >
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+ < td > Multiply by the reciprocal</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{21}{6} \cdot \dfrac{6}{28}$</ td >
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+ < td > Reduce $21$ and $28$ by dividing by $7.$ Reduce $6$ and $16$ by dividing by $2$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{3}{8} \cdot \dfrac{3}{4}$</ td >
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+ < td > Multiply numerators across and denominators across</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{9}{32}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ To add and subtract fractions we will first have to find the least common denominator
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+ (LCD). There are several ways to find an LCD. One way is to find the
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+ smallest multiple of the larger denominator that is also divisible by the smaller
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+ denominator.
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+
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+ < br > < br >
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+
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+ < b > Example 1A-5:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > Find the LCD of 8 and 12</ td >
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+ < td > Test multiples of 12</ td >
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+ </ tr >
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+ < tr >
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+ < td > $12?\dfrac{12}{8}$</ td >
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+ < td > No! Can't divide 12 by 8</ td >
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+ </ tr >
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+ < tr >
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+ < td > $24?\dfrac{24}{8}=3$</ td >
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+ < td > Yes! We can divide 24 by 8</ td >
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+ </ tr >
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+ < tr >
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+ < td > 24</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ Adding and subtracting fractions is identical in process. If both fractions already
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+ have a common denominator we just add or subtract the numerators and keep the
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+ denominator.
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+
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+ < br > < br >
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+
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+ < b > Example 1A-6:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{7}{8}+\dfrac{3}{8}$</ td >
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+ < td > Same denominator, add numerators $7+3$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{10}{8}$</ td >
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+ < td > Reduce answer, dividing by 2</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{5}{4}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ While $\dfrac{5}{4}$ can be written as the mixed number $1\dfrac{1}{4} , in algebra we will almost never
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+ use mixed numbers. For this reason we will always use the improper fraction, not
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+ the mixed number.
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+
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+ < br > < br >
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+
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+ < b > Example 1A-7:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{13}{6}-\dfrac{9}{6}$</ td >
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+ < td > Same denominator, subtract numerators $13-9$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{4}{6}$</ td >
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+ < td > Reduce answer, dividing by $2$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{2}{3}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+ If the denominators do not match we will first have to identify the LCD and build
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+ up each fraction by multiplying the numerators and denominators by the same
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+ number so the denominator is built up to the LCD.
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+
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+ < br > < br >
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+
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+ < b > Example 1A-8:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{5}{6}+\dfrac{4}{9}$</ td >
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+ < td > LCD is $18$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{3\cdot 5}{3\cdot 6}+\dfrac{4\cdot 2}{9\cdot 2}$</ td >
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+ < td > Multiply first fraction by $\dfrac{3}{3}$ and the second by $\dfrac{2}{2}$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{15}{18}+\dfrac{8}{18}$</ td >
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+ < td > Same denominator, add numerators, $15+8$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{23}{18}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br
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+
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+ < br > < br >
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+
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+ < b > Example 1A-9:</ b > < br >
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+ < table class = "center ">
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+ < tr >
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+ < td > $\dfrac{2}{3}-\dfrac{1}{6}$</ td >
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+ < td > LCD is $6$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{2\cdot 2}{2\cdot 3}-\dfrac{1}{6}$</ td >
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+ < td > Multiply first fraction by $\dfrac{2}{2}$, the second already has a denominator of $6$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{4}{6}-\dfrac{1}{6}$</ td >
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+ < td > Same denominator, subtract numerators, $4-1$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{3}{6}$</ td >
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+ < td > Reduce answer, dividing numerator and denominator by $3$</ td >
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+ </ tr >
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+ < tr >
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+ < td > $\dfrac{1}{2}$</ td >
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+ < td > Our solution</ td >
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+ </ tr >
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+ </ table >
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+ < br >
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+
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+
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+ </ body >
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+ </ html >
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