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Division is a process of sharing a quantity equally. In everyday life, quantities can be expressed as fractions instead of whole numbers. For example, a carpenter may need to cut a $541 -$foot piece of wood into $131 -$foot pieces. Here, the carpenter needs to divide the two fractions to find how many equal-length pieces they would get.
### Catch-Up and Review

$541 ÷131 =? $

In this lesson, similar problems will be solved to explain how to divide fractions. Additionaly, dividing fractions will be associated with multiplying fractions. Then they will be modeled by using visual fraction models. **Here are a few recommended readings before getting started with this lesson.**

Explore

The applet shows the multiplication of two numbers whose product is $1.$ What should be the second number?

Describe the relationship between the numbers.

Discussion

Two numbers are reciprocals, or multiplicative inverses, of each other when their product is the multiplicative identity. For example, the reciprocal of $9$ is $91 $ because their product is $1.$

Finding the reciprocal of a mixed number is like finding the reciprocal of a fraction. However, the mixed number must first be written as an improper fraction.

$9⋅91 =1 $

The reciprocal of a number $a$ can be found by dividing $1$ by $a.$ $Numbera Reciprocala1 $

Shortcuts exist to find the reciprocals of specific types of numbers such as natural numbers, integer numbers, fractions, and decimals.

Type | Reciprocal | Example |
---|---|---|

Natural number $a$ | $a1 $ | The reciprocal of $2$ is $21 .$ |

Integer numbers $a,$ $a =0$ | $a1 $ | The reciprocal of $-6$ is $-61 .$ |

Fraction $ba ,$ $b =0$ | $ab $ | The reciprocal of $23 $ is $32 .$ |

Decimal $a$ | $a1 $ | The reciprocal of $0.2$ is $0.21 .$ |

Discussion

Dividing a fraction by another fraction is the same as multiplying the first fraction by the reciprocal of the second fraction.

$ba ÷dc =ba ⋅cd $

$2512 ÷53 $

The quotient can be found in three steps.
1

Multiply by the Reciprocal of the Divisor

The division of fractions begins by keeping the first fraction as is. Then change the division sign with the multiplication sign and write the reciprocal of the second fraction. Note that the reciprocal of a fraction is found by switching the numerator and denominator of the fraction.

2

Multiply the Fractions

3

Simplfy if Possible

The resulting fraction can be simplified because $60$ and $75$ have a common factor.

$6075 =2_{2}⋅3⋅5=3⋅5_{2} $

The greatest common factor of the numbers is $3⋅5=15.$ Simplify the fraction by $15.$
The divison expression is equal to $54 .$ Example

Tearrik was gifted an heirloom by his grandfather. It is a handmade kimono.

Tearrik wants to make a box to hold this beautiful kimono. He plans to cut a piece of wood that is $5$ feet long. He wants the cuts to create equal parts.

External credits: textures.com

a How many $54 -$foot pieces can he cut from the original piece of wood?

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b There is one piece of wood remaining. What is its length?

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a Divide the length of the wood by the length of a smaller piece.

b Use the answer from Part A.

a Tearrik plans to cut the piece of wood into parts that are each $54 $ feet long.

External credits: textures.com

$5÷54 $

Dividing a whole number by a fraction is the same as multiplying that whole number by the reciprocal of the fraction. Recall the fact that all whole numbers are fractions whose denominator is $1.$
$5÷54 $

Rewrite

Rewrite $5$ as $15 $

$15 ÷54 $

DivFracByFracDiv

$ba ÷dc =ba ⋅cd $

$15 ⋅45 $

MultFrac

Multiply fractions

$1⋅45⋅5 $

Multiply

Multiply

$425 $

$425 $

WriteSum

Write as a sum

$424+1 $

WriteSumFrac

Write as a sum of fractions

$424 +41 $

CalcQuot

Calculate quotient

$6+41 $

Rewrite

Rewrite $6+41 $ as $641 $

$641 $

b In Part A, dividing $5$ into $54 $ was found to be $641 .$

$5÷54 =641 $

This finding is interpreted as Tearrik getting six $54 -$foot pieces. The remaining piece is $41 $ of a $54 -$foot piece. The length of the remaining piece of wood can be found by multiplying these fractions. $41 ×54 $

MultFrac

Multiply fractions

$4⋅51⋅4 $

CancelCommonFac

Cancel out common factors

$4 ⋅51⋅4 $

SimpQuot

Simplify quotient

$51 $

A diagram can be used to model the division of $5$ by $54 .$ Divide each foot of the $5-$foot-long wood into $5$ equal pieces.

External credits: textures.com

Notice that each of the smaller parts represents a $51 $ of a foot. Then determine how many of the $54 -$foot-long pieces are contained within the wood.

External credits: textures.com

There are $6$ of them. The length of the remaining part is a $51 $ of a foot. Note that the remaining part is also $41 $ of $54 .$ This confirms that the result found algebraically is correct.

Example

Tearrik is excited about making the box. A problem arises, however. He realizes a bit of paint would look cool but he does not have any in his home. Tearrik is full of energy and starts to run to the nearest paint shop.

External credits: macrovector

Tearrik runs $32 $ of the way from the garage to the nearest paint shop.

a If Tearriks runs $53 $ miles, find the distance between his home and the shop.

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b Tearrik buys $43 $ gallons of blue paint. He pours the paint evenly into $6$ cups. How many gallons of paint did he put in each cup?

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a Think about this question; $32 $ of what number is $53 ?$

b Divide the number of gallons by $6.$

a The distance Tearrik ran is given. He ran $32 $ of the way to the paint shop. This distance is equal to $53 $ of a mile.

$32 ofwhat numberis53 ? $

This question can be mathematically expressed as follows.
$32 ×? =53 $

Now, this multiplication problem can be written as a division problem.
$32 ×? =53 ⇔53 ÷32 =? $

The quotient of this division represents the distance to the paint shop. Consider that
dividing a fraction by a fraction is the same as multiplying the first fraction by the reciprocal of the second fraction.
$53 ÷32 $

DivFracByFracDiv

$ba ÷dc =ba ⋅cd $

$53 ⋅23 $

MultFrac

Multiply fractions

$5⋅23⋅3 $

Multiply

Multiply

$109 $

b The amount of blue paint Tearrik bought is a given, $43 $ gallons. He poured that amount evenly into $6$ cups. The diagram illustrates the total amount of paint and the unknown amount per cup.

$43 ÷6 $

This is a division of a fraction by a whole number. That means the whole number should be written as a fraction to calculate the quotient.
$43 ÷16 $

Now, the steps performed when dividing two fractions can be followed.
$43 ÷16 $

DivFracByFracDiv

$ba ÷dc =ba ⋅cd $

$43 ⋅61 $

MultFrac

Multiply fractions

$4⋅63⋅1 $

Multiply

Multiply

$243 $

$243 243 =3⋅83⋅1 ⇕=81 $

This means that Tearrik pours $81 $ gallon into each cup.
Pop Quiz

The applet shows random divisions involving fractions. Find the corresponding quotient of the given division. Simplify the answer to its lowest terms. If the answer is a whole number, write it as a fraction with a denominator of $1.$

Discussion

A division of fractions involving mixed numbers requires first writing the mixed numbers as improper fractions. Next, the same steps performed when dividing proper fractions can be followed. For example, consider the division of the following mixed numbers.
Now the usual steps can be used to find the quotient of these two fractions. The division sign is changed to a multiplication sign. Then the second fraction is replaced with its reciprocal.
The given quotient is $23 ,$ which can be rewritten as $121 .$

$351 ÷2152 $

First, the mixed numbers in this expression will be written as improper factions. Recall that a mixed number $acb $ is equal to $ca⋅c+b .$
$351 ÷2152 $

▼

Write mixed number as a fraction

$516 ÷1532 $

$516 ÷1532 $

DivFracByFracDiv

$ba ÷dc =ba ⋅cd $

$516 ⋅3215 $

▼

Evaluate

MultFrac

Multiply fractions

$5⋅3216⋅15 $

SplitIntoFactors

Split into factors

$5⋅16⋅216⋅5⋅3 $

CancelCommonFac

Cancel out common factors

$5 ⋅16⋅216⋅5 ⋅3 $

SimpQuot

Simplify quotient

$23 $

Example

Tearrik now has $6$ pieces of wood. Each piece has a length of $54 $ feet. The total area of the pieces is $153 $ square feet.

External credits: textures.com

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Start by finding the length of the greater rectangle. The result of multiplying the length of a small wood piece by $6,$ because there are $6$ pieces, will give the length of the rectangle.