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Mathematics LibreTexts

1.3: Fractions

  • Page ID
    5119
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    Summary

    By the end of this section, you will be able to:

    • Simplify fractions
    • Multiply and divide fractions
    • Add and subtract fractions
    • Use the order of operations to simplify fractions
    • Evaluate variable expressions with fractions

    A more thorough introduction to the topics covered in this section can be found in the Elementary Algebra chapter, Foundations.

    Simplify Fractions

    A fraction is a way to represent parts of a whole. The fraction \(\frac{2}{3}\) represents two of three equal parts (Figure \(\PageIndex{1}\)). In the fraction \(\frac{2}{3}\), the 2 is called the numerator and the 3 is called the denominator. The line is called the fraction bar.

    Figure shows a circle divided in three equal parts. 2 of these are shaded.
    Figure \(\PageIndex{1}\): In the circle, \(\frac{2}{3}\) of the circle is shaded—2 of the 3 equal parts.

    FRACTION

    A fraction is written \(\frac{a}{b}\), where \(b\neq 0\) and

    \(\textit{a}\) is the numerator and \(\textit{b}\) is the denominator.

    A fraction represents parts of a whole. The denominator \(\textit{b}\) is the number of equal parts the whole has been divided into, and the numerator \(\textit{a}\) indicates how many parts are included.

    Fractions that have the same value are equivalent fractions. The Equivalent Fractions

    Property allows us to find equivalent fractions and also simplify fractions.

    EQUIVALENT FRACTIONS PROPERTY

    If \(\textit{a}\), \(\textit{b}\), and \(\textit{c}\) are numbers where \(b\neq 0,c\neq 0\),

    then \(\frac{a}{b}=\frac{a·c}{b·c}\) and \(\frac{a·c}{b·c}=\frac{a}{b}.\)

    A fraction is considered simplified if there are no common factors, other than 1, in its numerator and denominator.

    For example,

    \(\frac{2}{3}\) is simplified because there are no common factors of \(2\) and \(\textbf{3.}\)

    \(\frac{10}{15}\) is not simplified because \(5\) is a common factor of \(10\) and \(\textbf{15.}\)

    We simplify, or reduce, a fraction by removing the common factors of the numerator and denominator. A fraction is not simplified until all common factors have been removed. If an expression has fractions, it is not completely simplified until the fractions are simplified.

    Sometimes it may not be easy to find common factors of the numerator and denominator. When this happens, a good idea is to factor the numerator and the denominator into prime numbers. Then divide out the common factors using the Equivalent Fractions Property.

    EXAMPLE \(\PageIndex{1}\): How To Simplify a Fraction

    Simplify \(\frac{−315}{770}\).

    Answer

    Step 1 is to rewrite the numerator and denominator to show the common factors. If needed, use a factor tree. Here, we rewrite 315 and 770 as the product of the primes. Starting with minus 315 divided by 770, we get, minus 3 times 3 time 5 times 7 divided by 2 times 5 times 7 times 11.

    Step 2 is to simplify using the Equivalent Fractions Property by dividing out common factors. We first mark out the common factors 5 and 7 and then divide them out. This leaves minus 3 times 3 divided by 2 times 11.

    Step 3 is to multiply the remaining factors, if necessary. We get minus 9 by 22.

    EXAMPLE \(\PageIndex{2}\)

    Simplify \(−\frac{69}{120}\).

    Answer

    \(−\frac{23}{40}\)

    EXAMPLE \(\PageIndex{3}\)

    Simplify \(−\frac{120}{192}\).

    Answer

    \(−\frac{5}{8}\)

    We now summarize the steps you should follow to simplify fractions.

    SIMPLIFY A FRACTION.

    1. Rewrite the numerator and denominator to show the common factors.
      If needed, factor the numerator and denominator into prime numbers first.
    2. Simplify using the Equivalent Fractions Property by dividing out common factors.
    3. Multiply any remaining factors.

    Multiply and Divide Fractions

    Many people find multiplying and dividing fractions easier than adding and subtracting fractions.

    To multiply fractions, we multiply the numerators and multiply the denominators.

    FRACTION MULTIPLICATION

    If a, b, c, and d are numbers where \(b≠0\), and \(d≠0\), then

    \[\frac{a}{b}·\frac{c}{d}=\frac{ac}{bd}\]

    To multiply fractions, multiply the numerators and multiply the denominators.

    When multiplying fractions, the properties of positive and negative numbers still apply, of course. It is a good idea to determine the sign of the product as the first step. In Example, we will multiply negative and a positive, so the product will be negative.

    When multiplying a fraction by an integer, it may be helpful to write the integer as a fraction. Any integer, a, can be written as \(\frac{a}{1}\). So, for example, \(3=\frac{3}{1}\).

    Exercise \(\PageIndex{4}\)

    Multiply: \(−\frac{12}{5}(−20x).\)

    Answer

    The first step is to find the sign of the product. Since the signs are the same, the product is positive.

     

    Determine the sign of the product. The signs are the same, so the product is positive.

     

    Write 20x as a fraction.
    Multiply.

    Rewrite 20 to show the common factor 5 and divide it out.

     

    Simplify.

    Exercise \(\PageIndex{5}\)

    Multiply: \(\frac{1}{13}(−9a)\).

    Answer

    \(−33a\)

    Exercise \(\PageIndex{6}\)

    Multiply: \(\frac{13}{7}(−14b)\).

    Answer

    \(−26b\)

    Now that we know how to multiply fractions, we are almost ready to divide. Before we can do that, we need some vocabulary. The reciprocal of a fraction is found by inverting the fraction, placing the numerator in the denominator and the denominator in the numerator. The reciprocal of \(\frac{2}{3}\) is \(\frac{3}{2}\). Since 4 is written in fraction form as \(\frac{4}{1}\), the reciprocal of 4 is \(\frac{1}{4}\).

    To divide fractions, we multiply the first fraction by the reciprocal of the second.

    FRACTION DIVISION

    If a, b, c, and d are numbers where \(b≠0\),\(c≠0\), and \(d≠0\), then

    \[\frac{a}{b}÷\frac{c}{d}=\frac{a}{b}⋅\frac{d}{c}\]

    To divide fractions, we multiply the first fraction by the reciprocal of the second.

    We need to say \(b≠0\), \(c≠0\), and \(d≠0\), to be sure we don’t divide by zero!

    Exercise \(\PageIndex{7}\)

    Find the quotient: \(−\frac{7}{18}÷(−\frac{14}{27}).\)

    Answer
      \(−\frac{7}{18}÷(−\frac{14}{27})\)

    To divide, multiply the first fraction by the reciprocal of the second.

    Determine the sign of the product, and then multiply.

    Rewrite showing common factors.
    Remove common factors.
    Simplify.

    Exercise \(\PageIndex{8}\)

    Divide: \(−\frac{7}{27}÷(−\frac{35}{36})\).

    Answer

    \(\frac{4}{15}\)

    Exercise \(\PageIndex{9}\)

    Divide: \(−\frac{5}{14}÷(−\frac{15}{28}).\)

    Answer

    \(\frac{2}{3}\)

    The numerators or denominators of some fractions contain fractions themselves. A fraction in which the numerator or the denominator is a fraction is called a complex fraction.

    Definition: COMPLEX FRACTION

    A complex fraction is a fraction in which the numerator or the denominator contains a fraction.

    Some examples of complex fractions are:

    \[\frac{\frac{6}{7}}{3} \; \; \; \; \; \; \frac{\frac{3}{4}}{\frac{5}{8}} \; \; \; \; \; \; \frac{\frac{x}{2}}{ \frac{5}{6}}\]

    To simplify a complex fraction, remember that the fraction bar means division. For example, the complex fraction \(\frac{\frac{3}{4}}{\frac{5}{8}}\) means \(\frac{3}{4}÷\frac{5}{8}.\)

    Exercise \(\PageIndex{10}\)

    Simplify: \(\frac{\frac{x}{2}}{ \frac{xy}{6}}\).

    Answer

    \(\begin{array}{lc} \text{} & \frac{\frac{x}{2}}{ \frac{xy}{6}} \\ \text{Rewrite as division.} & \frac{x}{2}÷\frac{xy}{6} \\ \text{Multiply the first fraction by the reciprocal of the second.} & \frac{x}{2}·\frac{6}{xy} \\ \text{Multiply.} & \frac{x·6}{2·xy} \\ \text{Look for common factors.} & \frac{ \cancel{x}·3·\cancel{2}}{\cancel{2}·\cancel{x}·y} \\ \text{Divide common factors and simplify.} & \frac{3}{y} \end{array}\)

    Exercise \(\PageIndex{11}\)

    Simplify: \(\frac{\frac{a}{8}}{ \frac{ab}{6}}\).

    Answer

    \(\frac{3}{4b}\)

    Exercise \(\PageIndex{12}\)

    Simplify: \(\frac{\frac{p}{2}}{ \frac{pq}{8}}\).

    Answer

    \(\frac{4}{q}\)

    Add and Subtract Fractions

    When we multiplied fractions, we just multiplied the numerators and multiplied the denominators right straight across. To add or subtract fractions, they must have a common denominator.

    FRACTION ADDITION AND SUBTRACTION

    If a, b, and c are numbers where \(c≠0\), then

    \[\dfrac{a}{c}+\dfrac{b}{c}=\dfrac{a+b}{c} \text{ and } \dfrac{a}{c}−\dfrac{b}{c}=\dfrac{a−b}{c}\]

    To add or subtract fractions, add or subtract the numerators and place the result over the common denominator.

    The least common denominator (LCD) of two fractions is the smallest number that can be used as a common denominator of the fractions. The LCD of the two fractions is the least common multiple (LCM) of their denominators.

    LEAST COMMON DENOMINATOR

    The least common denominator (LCD) of two fractions is the least common multiple (LCM) of their denominators.

    After we find the least common denominator of two fractions, we convert the fractions to equivalent fractions with the LCD. Putting these steps together allows us to add and subtract fractions because their denominators will be the same!

    EXAMPLE \(\PageIndex{13}\): How to Add or Subtract Fractions

    Add: \(\frac{7}{12}+\frac{5}{18}\).

    Answer

    The expression is 7 by 12 plus 5 by 18. Step 1 is to check if the two numbers have a common denominator. Since they do not, rewrite each fraction with the LCD (least common denominator). For finding the LCD, we write the factors of 12 as 2 times 2 times 2 and the factors of 18 as 2 times 3 times 3. The LCD is 2 times 2 times 3 times 3, which is equal to 36.

    Step 2 is to add or subtract the fractions. We multiply the numerator and denominator of each fraction by the factor needed to get the denominator to be 36. Do not simplify the equivalent fractions. If you do, you’ll get back to the original fractions and lose the common denominator. We multiply the numerator and denominator of 7 divided by 12, by 3 times. We multiply numerator and denominator of 5 divided by 18 by 2 times. We get the expression 21 by 36 plus 10 by 36.

    Step 3 is to simplify is possible. Since 31 is prime, its only factors are 1and 31. Since 31 does not go into 36, the answer is simplified.

    EXAMPLE \(\PageIndex{14}\)

    Add: \(\frac{7}{12}+\frac{11}{15}\).

    Answer

    \(\frac{79}{60}\)

    EXAMPLE \(\PageIndex{15}\)

    Add: \(\frac{13}{15}+\frac{17}{20}\).

    Answer

    \(\frac{103}{60}\)

    ADD OR SUBTRACT FRACTIONS.

    1. Do they have a common denominator?
      • Yes—go to step 2.
      • No—rewrite each fraction with the LCD (least common denominator).
        • Find the LCD.
        • Change each fraction into an equivalent fraction with the LCD as its denominator.
    2. Add or subtract the fractions.
    3. Simplify, if possible.
     

    We now have all four operations for fractions. Table summarizes fraction operations.

    Fraction Multiplication Fraction Division
    \(\frac{a}{b}⋅\frac{c}{d}=\frac{ac}{bd}\) \(\frac{a}{b}÷\frac{c}{d}=\frac{a}{b}⋅\frac{d}{c}\)
    Multiply the numerators and multiply the denominators Multiply the first fraction by the reciprocal of the second.
    Fraction Addition Fraction Subtraction
    \(\frac{a}{c}+\frac{b}{c}=\frac{a+b}{c}\) \(\frac{a}{c}−\frac{b}{c}=\frac{a−b}{c}\)
    Add the numerators and place the sum over the common denominator. Subtract the numerators and place the difference over the common denominator.

    To multiply or divide fractions, an LCD is NOT needed.

     

    To add or subtract fractions, an LCD is needed.

    When starting an exercise, always identify the operation and then recall the methods needed for that operation.

    EXAMPLE \(\PageIndex{16}\)

    Simplify: ⓐ \(\frac{5x}{6}−\frac{3}{10}\) ⓑ \(\frac{5x}{6}·\frac{3}{10}\).

    Answer

    First ask, “What is the operation?” Identifying the operation will determine whether or not we need a common denominator. Remember, we need a common denominator to add or subtract, but not to multiply or divide.

    \(\begin{array}{lc} \text{What is the operation? The operation is subtraction.} \\ \text{Do the fractions have a common denominator? No.} & \frac{5x}{6} − \frac{3}{10} \\ \text{Find the LCD of }6 \text{ and }10 & \text{The LCD is 30.}\\ {\begin{align} 6 & =2·3 \\ \; \; \underline{\; \; \; \; 10 \; \; \; \; } & \underline{=2·5 \; \; \; \;} \; \\ \text{LCD} & =2·3·5 \\ \text{LCD} & =30 \end{align}} \\ \\ \\ \text{Rewrite each fraction as an equivalent fraction with the LCD.} & \frac{5x·5}{6·5}−\frac{3·3}{10·3}\\ \text{} & \frac{25x}{30}−\frac{9}{30} \\ \text{Subtract the numerators and place the} \\ \text{difference over the common denominators.} & \frac{25x−9}{30} \\ \\ \\ \text{Simplify,if possible.There are no common factors.} \\ \text{The fraction is simplified.} \end{array}\)

    \(\begin{array}{lc} \text{What is the operation? Multiplication.} & \frac{25x}{6}·\frac{3}{10} \\ \text{To multiply fractions,multiply the numerators} \\ \text{and multiply the denominators.} & \frac{25x·3}{6·10} \\ \text{Rewrite, showing common factors.} \\ \text{Remove common factors.} & \frac{\cancel{5} x · \cancel{3}}{2·\cancel{3}·2·\cancel{5}} \\ \text{Simplify.} & \frac{x}{4} \end{array}\)

    Notice, we needed an LCD to add \(\frac{25x}{6}−\frac{3}{10}\), but not to multiply \(\frac{25x}{6}⋅\frac{3}{10}\).

    EXAMPLE \(\PageIndex{17}\)

    Simplify: ⓐ \(\frac{3a}{4}−\frac{8}{9}\) ⓑ \(\frac{3a}{4}·\frac{8}{9}\).

    Answer

    ⓐ \(\frac{27a−32}{36}\) ⓑ \(\frac{2a}{3}\)

    EXAMPLE \(\PageIndex{18}\)

    Simplify: ⓐ\(\frac{4k}{5}−\frac{1}{6}\) ⓑ \(\frac{4k}{5}⋅\frac{1}{6}\).

    Answer

    ⓐ \(\frac{24k−5}{30}\) ⓑ \(\frac{2k}{15}\)

    Use the Order of Operations to Simplify Fractions

    The fraction bar in a fraction acts as grouping symbol. The order of operations then tells us to simplify the numerator and then the denominator. Then we divide.

    SIMPLIFY AN EXPRESSION WITH A FRACTION BAR.

    1. Simplify the expression in the numerator. Simplify the expression in the denominator.
    2. Simplify the fraction.

    Where does the negative sign go in a fraction? Usually the negative sign is in front of the fraction, but you will sometimes see a fraction with a negative numerator, or sometimes with a negative denominator. Remember that fractions represent division. When the numerator and denominator have different signs, the quotient is negative.

    \[\dfrac{−1}{3}=−\dfrac{1}{3} \; \; \; \; \; \; \dfrac{\text{negative}}{\text{positive}}=\text{negative}\]

    \[\dfrac{1}{−3}=−\dfrac{1}{3} \; \; \; \; \; \; \dfrac{\text{positive}}{\text{negative}}=\text{negative}\]

    PLACEMENT OF NEGATIVE SIGN IN A FRACTION

    For any positive numbers a and b,

    \[\dfrac{−a}{b}=\dfrac{a}{−b}=−\dfrac{a}{b}\]

    EXAMPLE \(\PageIndex{19}\)

    Simplify: \(\frac{4(−3)+6(−2)}{−3(2)−2}\).

    Answer

    The fraction bar acts like a grouping symbol. So completely simplify the numerator and the denominator separately.

    \(\begin{array}{lc} \text{} & \frac{4(−3)+6(−2)}{−3(2)−2} \\ \text{Multiply.} & \frac{−12+(−12)}{−6−2} \\ \text{Simplify.} & \frac{−24}{−8} \\ \text{Divide.} & 3 \end{array}\)

    EXAMPLE \(\PageIndex{20}\)

    Simplify:\(\frac{8(−2)+4(−3)}{−5(2)+3}\).

    Answer

    4

    EXAMPLE \(\PageIndex{21}\)

    Simplify: \(\frac{7(−1)+9(−3)}{−5(3)−2}\).

    Answer

    2

    Now we’ll look at complex fractions where the numerator or denominator contains an expression that can be simplified. So we first must completely simplify the numerator and denominator separately using the order of operations. Then we divide the numerator by the denominator as the fraction bar means division.

    EXAMPLE \(\PageIndex{22}\): How to Simplify Complex Fractions

    Simplify: \(\frac{(\frac{1}{2})^2}{4+3^2}\).

    Answer

    The expression is 1 by 2 the whole squared divided by 4 plus 3 squared. Step 1 is to simplify the numerator, which becomes 1 by 4.

    Step 2 is to simplify the denominator, which becomes 4 plus 9 equals 13.

    Step 3 is to divide the numerator by the denominator and simplify if possible. Now the expression becomes 1 by 4 divided by 13 by 1, which equals 1 by 4 multiplied by 1 by 13, which equals 1 by 52

    EXAMPLE \(\PageIndex{23}\)

    Simplify: \((\frac{\frac{1}{3})^2}{2^3+2})\).

    Answer

    \(\frac{1}{90}\)

    EXAMPLE \(\PageIndex{24}\)

    Simplify: \(\frac{1+4^2}{(\frac{1}{4})^2}\).

    Answer

    272

    SIMPLIFY COMPLEX FRACTIONS.

    1. Simplify the numerator.
    2. Simplify the denominator.
    3. Divide the numerator by the denominator. Simplify if possible.

    EXAMPLE \(\PageIndex{25}\)

    Simplify: \(\frac{\frac{1}{2}+\frac{2}{3}}{\frac{3}{4}−\frac{1}{6}}\).

    Answer

    It may help to put parentheses around the numerator and the denominator.

    \(\begin{array}{lc}\text{} & \frac{\frac{1}{2}+\frac{2}{3}}{\frac{3}{4}−\frac{1}{6}} \\ \text{Simplify the numerator }(LCD=6)\text{ and } \\ \text{simplify the denominator }(LCD=12). & \frac{(\frac{3}{6}+\frac{4}{6})}{(\frac{9}{12}−\frac{2}{12})} \\ \text{Simplify.} & (\frac{7}{6})(\frac{7}{12}) \\ \text{Divide the numerator by the denominator.} & \frac{7}{6}÷\frac{7}{12} \\ \text{Simplify.} & \frac{7}{6}⋅\frac{12}{7} \\ \text{Divide out common factors.} & \frac{\cancel{7}⋅\cancel{6}⋅2}{ \cancel{6}⋅\cancel{7}⋅1} \\ \text{Simplify.} & 2 \end{array}\)

    EXAMPLE \(\PageIndex{26}\)

    Simplify: \( \frac{\frac{1}{3}+\frac{1}{2}}{ \frac{3}{4}−\frac{1}{3}}\).

    Answer

    2

    EXAMPLE \(\PageIndex{27}\)

    Simplify: \(\frac{\frac{2}{3}−\frac{1}{2}}{ \frac{1}{4}+\frac{1}{3}}\).

    Answer

    \(\frac{2}{7}\)

    Evaluate Variable Expressions with Fractions

    We have evaluated expressions before, but now we can evaluate expressions with fractions. Remember, to evaluate an expression, we substitute the value of the variable into the expression and then simplify.

    EXAMPLE \(\PageIndex{28}\)

    Evaluate \(2x^2y\) when \(x=\frac{1}{4}\) and \(y=−\frac{2}{3}\).

    Answer

    Substitute the values into the expression.

     
    Simplify exponents first.
    Multiply; divide out the common factors. Notice we write 16 as 2⋅2⋅42·2·4 to make it easy to remove common factors.
    Simplify.

    EXAMPLE \(\PageIndex{29}\)

    Evaluate \(3ab^2\) when \(a=−\frac{2}{3}\) and \(b=−\frac{1}{2}\).

    Answer

    \(−\frac{1}{2}\)

    EXAMPLE \(\PageIndex{30}\)

    Evaluate \(4c^3d\) when \(c=−\frac{1}{2}\) and \(d=−\frac{4}{3}\).

    Answer

    \(\frac{2}{3}\)

    Access this online resource for additional instruction and practice with fractions.

    Key Concepts

    • Equivalent Fractions Property

      If a, b, and c are numbers where \(b≠0,c≠0\), then

    \(\frac{a}{b}=\frac{a·c}{b·c}\) and \(\frac{a·c}{b·c}=\frac{a}{b}.\)

    • How to simplify a fraction.
      1. Rewrite the numerator and denominator to show the common factors.
        If needed, factor the numerator and denominator into prime numbers first.
      2. Simplify using the Equivalent Fractions Property by dividing out common factors.
      3. Multiply any remaining factors.
    • Fraction Multiplication

      If a, b, c, and d are numbers where \(b≠0\), and \(d≠0\), then

      \(\frac{a}{b}·\frac{c}{d}=\frac{ac}{bd}\)

      To multiply fractions, multiply the numerators and multiply the denominators.

    • Fraction Division

      If a, b, c, and d are numbers where \(b≠0\),\(c≠0\), and \(d≠0\), then

      \(\frac{a}{b}÷\frac{c}{d}=\frac{a}{b}⋅\frac{d}{c}\)

      To divide fractions, we multiply the first fraction by the reciprocal of the second.

    • Fraction Addition and Subtraction

      If a, b, and c are numbers where \(c≠0\), then

      \(\frac{a}{c}+\frac{b}{c}=\frac{a+b}{c} \text{ and } \frac{a}{c}−\frac{b}{c}=\frac{a−b}{c}\)

      To add or subtract fractions, add or subtract the numerators and place the result over the common denominator.

    • How to add or subtract fractions.
      1. Do they have a common denominator?
        • Yes—go to step 2.
        • No—rewrite each fraction with the LCD (least common denominator).
          • Find the LCD.
          • Change each fraction into an equivalent fraction with the LCD as its denominator.
      2. Add or subtract the fractions.
      3. Simplify, if possible.
    • How to simplify an expression with a fraction bar.
      1. Simplify the expression in the numerator. Simplify the expression in the denominator.
      2. Simplify the fraction.
    • Placement of Negative Sign in a Fraction

      For any positive numbers a and b,

      \(\frac{−a}{b}=\frac{a}{−b}=−\frac{a}{b}\)

    • How to simplify complex fractions.
      1. Simplify the numerator.
      2. Simplify the denominator.
      3. Divide the numerator by the denominator. Simplify if possible.

    Practice Makes Perfect

    Simplify Fractions

    In the following exercises, simplify.

    \(−\frac{108}{63}\)

    Answer

    \(−\frac{12}{7}\)

    \(−\frac{104}{48}\)

    \(\frac{120}{252}\)

    Answer

    \(\frac{10}{21}\)

    \(\frac{182}{294}\)

    \(\frac{14x^2}{21y}\)

    Answer

    \(\frac{2x^2}{3y}\)

    \(\frac{24a}{32b^2}\)

    \(−\frac{210a^2}{110b^2}\)

    Answer

    \(−\frac{21a^2}{11b^2}\)

    \(−\frac{30x^2}{105y^2}\)

    Multiply and Divide Fractions

    In the following exercises, perform the indicated operation.

    \(−\frac{3}{4}(−\frac{4}{9})\)

    Answer

    \(\frac{1}{3}\)

    \(−\frac{3}{8}⋅\frac{4}{15}\)

    \((−\frac{14}{15})(\frac{9}{20})\)

    Answer

    \(−\frac{21}{50}\)

    \((−\frac{9}{10})(\frac{25}{33})\)

    \((−\frac{63}{84})(−\frac{44}{90})\)

    Answer

    \(\frac{11}{30}\)

    \((−\frac{33}{60})(−\frac{40}{88})\)

    \(\frac{3}{7}⋅21n\)

    Answer

    \(9n\)

    \(\frac{5}{6}⋅30m\)

    \(\frac{3}{4}÷\frac{x}{11}\)

    Answer

    \(\frac{33}{4x}\)

    \(\frac{2}{5}÷\frac{y}{9}\)

    \(\frac{5}{18}÷(−\frac{15}{24})\)

    Answer

    \(−\frac{4}{9}\)

    \(\frac{7}{18}÷(−\frac{14}{27})\)

    \(\frac{8u}{15}÷\frac{12v}{25}\)

    Answer

    \(\frac{10u}{9v}\)

    \(\frac{12r}{25}÷\frac{18s}{35}\)

    \(\frac{3}{4}÷(−12)\)

    Answer

    \(−\frac{1}{16}\)

    \(−15÷(−\frac{5}{3})\)

    In the following exercises, simplify.

    \(−\frac{\frac{8}{21} }{\frac{12}{35}}\)

    Answer

    \(−\frac{10}{9}\)

    \(− \frac{\frac{9}{16} }{\frac{33}{40}}\)

    \(−\frac{\frac{4}{5}}{2}\)

    Answer

    \(−\frac{2}{5}\)

    \(\frac{\frac{5}{3}}{10}\)

    \(\frac{\frac{m}{3}}{\frac{n}{2}}\)

    Answer

    \(\frac{2m}{3n}\)

    \(\frac{−\frac{3}{8}}{−\frac{y}{12}}\)

    Add and Subtract Fractions

    In the following exercises, add or subtract.

    \(\frac{7}{12}+\frac{5}{8}\)

    Answer

    \(\frac{29}{24}\)

    \(\frac{5}{12}+\frac{3}{8}\)

    \(\frac{7}{12}−\frac{9}{16}\)

    Answer

    \(\frac{1}{48}\)

    \(\frac{7}{16}−\frac{5}{12}\)

    \(−\frac{13}{30}+\frac{25}{42}\)

    Answer

    \(\frac{17}{105}\)

    \(−\frac{23}{30}+\frac{5}{48}\)

    \(−\frac{39}{56}−\frac{22}{35}\)

    Answer

    \(−\frac{53}{40}\)

    \(−\frac{33}{49}−\frac{18}{35}\)

    \(−\frac{2}{3}−(−\frac{3}{4})\)

    Answer

    \(\frac{1}{12}\)

    \(−\frac{3}{4}−(−\frac{4}{5})\)

    \(\frac{x}{3}+\frac{1}{4}\)

    Answer

    \(\frac{4x+3}{12}\)

    \(\frac{x}{5}−\frac{1}{4}\)

    ⓐ \(\frac{2}{3}+\frac{1}{6}\)

    ⓑ \(\frac{2}{3}÷\frac{1}{6}\)

    Answer

    ⓐ \(\frac{5}{6}\)ⓑ \(4\)

    ⓐ \(−\frac{2}{5}−\frac{1}{8}\)

    ⓑ \(−\frac{2}{5}·\frac{1}{8}\)

    ⓐ \(\frac{5n}{6}÷\frac{8}{15}\)

    ⓑ \(\frac{5n}{6}−\frac{8}{15}\)

    Answer

    ⓐ \(\frac{25n}{16}\) ⓑ \(\frac{25n−16}{30}\)

    ⓐ \(\frac{3a}{8}÷\frac{7}{12}\)

    ⓑ \(\frac{3a}{8}−\frac{7}{12}\)

    ⓐ \(−\frac{4x}{9}−\frac{5}{6}\)

    ⓑ \(−\frac{4k}{9}⋅\frac{5}{6}\)

     
    Answer

    ⓐ \(\frac{−8x−15}{18}\) ⓑ \(−\frac{10k}{27}\)

    ⓐ \(−\frac{3y}{8}−\frac{4}{3}\)

    ⓑ \(−\frac{3y}{8}⋅\frac{4}{3}\)

    ⓐ \(−\frac{5a}{3}+(−\frac{10}{6})\)

    ⓑ \(−\frac{5a}{3}÷(−\frac{10}{6})\)

     
    Answer

    ⓐ \(\frac{−5(a+1)}{3}\) ⓑ \(a\)

    ⓐ \(\frac{2b}{5}+\frac{8}{15}\)

    ⓑ \(\frac{2b}{5}÷\frac{8}{15}\)

    Use the Order of Operations to Simplify Fractions

    In the following exercises, simplify.

    \(\frac{5⋅6−3⋅4}{4⋅5−2⋅3}\)

    Answer

    \(\frac{9}{7}\)

    \(\frac{8⋅9−7⋅6}{5⋅6−9⋅2}\)

    \(\frac{5^2−3^2}{3−5}\)

    Answer

    \(−8\)

    \(\frac{6^2−4^2}{4−6}\)

    \(\frac{7⋅4−2(8−5)}{9⋅3−3⋅5}\)

    Answer

    \(\frac{11}{6}\)

    \(\frac{9⋅7−3(12−8)}{8⋅7−6⋅6}\)

    \(\frac{9(8−2)−3(15−7)}{6(7−1)−3(17−9)}\)

    Answer

    \(\frac{5}{2}\)

    \(\frac{8(9−2)−4(14−9)}{7(8−3)−3(16−9)}\)

    \(\frac{2^3+4^2}{(\frac{2}{3})^2}\)

    Answer

    \(54\)

    \(\frac{3^3−3^2}{(\frac{3}{4})^2}\)

    \(\frac{(\frac{3}{5})^2}{(\frac{3}{7})^2}\)

    Answer

    \(\frac{49}{25}\)

    \(\frac{(\frac{3}{4})^2}{(\frac{5}{8})^2}\)

    \(\frac{2}{\frac{1}{3}+\frac{1}{5}}\)

    Answer

    \(\frac{15}{4}\)

    \(\frac{5}{\frac{1}{4}+\frac{1}{3}}\)

    \(\frac{\frac{7}{8}−\frac{2}{3}}{\frac{1}{2}+\frac{3}{8}}\)

     
    Answer

    \(\frac{5}{21}\)

    \(\frac{\frac{3}{4}−\frac{3}{5}}{\frac{1}{4}+\frac{2}{5}}\)

    Mixed Practice

    In the following exercises, simplify.

    \(−\frac{3}{8}÷(−\frac{3}{10})\)

    Answer

    \(\frac{5}{4}\)

    \(−\frac{3}{12}÷(−\frac{5}{9})\)

    \(−\frac{3}{8}+\frac{5}{12}\)

    Answer

    \(\frac{1}{24}\)

    \(−\frac{1}{8}+\frac{7}{12}\)

    \(−\frac{7}{15}−\frac{y}{4}\)

    Answer

    \(\frac{−28−15y}{60}\)

    \(−\frac{3}{8}−\frac{x}{11}\)

    \(\frac{11}{12a}⋅\frac{9a}{16}\)

    Answer

    \(\frac{33}{64}\)

    \(\frac{10y}{13}⋅\frac{8}{15y}\)

    \(\frac{1}{2}+\frac{2}{3}⋅\frac{5}{12}\)

    Answer

    \(\frac{7}{9}\)

    \(\frac{1}{3}+\frac{2}{5}⋅\frac{3}{4}\)

    \(1−\frac{3}{5}÷\frac{1}{10}\)

    Answer

    \(−5\)

    \(1−\frac{5}{6}÷\frac{1}{12}\)

    ​​​​​​​

    \(\frac{3}{8}−\frac{1}{6}+\frac{3}{4}\)

    Answer

    \(\frac{23}{24}\)

     

    \(\frac{2}{5}+\frac{5}{8}−\frac{3}{4}\)

    ​​​​​​​​​​​​​​

    \(12(\frac{9}{20}−\frac{4}{15})\)

    Answer

    \(\frac{11}{5}\)

    \(8(\frac{15}{16}−\frac{5}{6})\)

    ​​​​​​​​​​​​​​

    \(\frac{\frac{5}{8}+\frac{1}{6}}{\frac{19}{24}}\)

    Answer

    \(1\)

    \(\frac{\frac{1}{6}+\frac{3}{10}}{\frac{14}{30}}\)

    ​​​​​​​​​​​​​​

    \((\frac{5}{9}+\frac{1}{6})÷(\frac{2}{3}−\frac{1}{2})\)

    Answer

    \(\frac{13}{3}\)

    \((\frac{3}{4}+\frac{1}{6})÷(\frac{5}{8}−\frac{1}{3})\)

    Evaluate Variable Expressions with Fractions

    In the following exercises, evaluate.

    \(\frac{7}{10}−w\) when

    ⓐ \(w=\frac{1}{2}\) ⓑ \(w=−\frac{1}{2}\)

    Answer

    ⓐ \(\frac{1}{5}\) ⓑ \(\frac{6}{5}\)

    512−w when

    ⓐ \(w=\frac{1}{4}\) ⓑ \(w=−\frac{1}{4}\)

    ​​​​​​​​​​​​​​

    \(2x^2y^3\) when

    \(x=−\frac{2}{3}\) and \(y=−\frac{1}{2}\)

    Answer

    \(−\frac{1}{9}\)

    \(8u^2v^3\) when

    \(u=−\frac{3}{4}\) and \(v=−\frac{1}{2}\)

    ​​​​​​​​​​​​​​

    \(\frac{a+b}{a−b}\) when

    \(a=−3,b=8\)

    Answer

    \(−\frac{5}{11}\)

    \(\frac{r−s}{r+s}\) when

    \(r=10,s=−5\)

     

    Writing Exercises

    Why do you need a common denominator to add or subtract fractions? Explain.

    Answer

    Answers will vary.

    How do you find the LCD of 2 fractions?

    Explain how you find the reciprocal of a fraction.

    Answer

    Answers will vary.

    Explain how you find the reciprocal of a negative number.

    Self Check

    ⓐ After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

    This table has 4 columns, 5 rows and a header row. The header row labels each column I can, confidently, with some help and no, I don’t get it. The first column has the following statements: simplify fractions, multiply and divide fractions, add and subtract fractions, use the order of operations to simplify fractions, evaluate variable expressions with fractions. The remaining columns are blank.

    ⓑ What does this checklist tell you about your mastery of this section? What steps will you take to improve?

    Glossary

    complex fraction
    A fraction in which the numerator or the denominator is a fraction is called a complex fraction.
    denominator
    In a fraction, written \(\frac{a}{b}\), where \(b≠0\), the denominator b is the number of equal parts the whole has been divided into.
    equivalent fractions
    Equivalent fractions are fractions that have the same value.
    fraction
    A fraction is written \(\frac{a}{b}\), where \(b≠0\), and a is the numerator and b is the denominator. A fraction represents parts of a whole.
    least common denominator
    The least common denominator (LCD) of two fractions is the least common multiple (LCM) of their denominators.
    numerator
    In a fraction, written \(\frac{a}{b}\), where \(b≠0\), the numerator a indicates how many parts are included.
    reciprocal
    The reciprocal of a fraction is found by inverting the fraction, placing the numerator in the denominator and the denominator in the numerator.