Elementary Algebra 2e — Original English

Visualize Fractions

Find Equivalent Fractions

Fractions are a way to represent parts of a whole. The fraction 13 means that one whole has been divided into 3 equal parts and each part is one of the three equal parts. See Figure 1. The fraction 23 represents two of three equal parts. In the fraction 23, the 2 is called the numerator and the 3 is called the denominator.

Two circles are shown, each divided into three equal pieces by lines. The left hand circle is labeled “one third” in each section. Each section is shaded. The circle on the right is shaded in two of its three sections.
The circle on the left has been divided into 3 equal parts. Each part is 13 of the 3 equal parts. In the circle on the right, 23 of the circle is shaded (2 of the 3 equal parts).

If a whole pie has been cut into 6 pieces and we eat all 6 pieces, we ate 66 pieces, or, in other words, one whole pie.

A circle is shown and is divided into six section. All sections are shaded.

So 66=1. This leads us to the property of one that tells us that any number, except zero, divided by itself is 1.

If a pie was cut in 6 pieces and we ate all 6, we ate 66 pieces, or, in other words, one whole pie. If the pie was cut into 8 pieces and we ate all 8, we ate 88 pieces, or one whole pie. We ate the same amount—one whole pie.

The fractions 66 and 88 have the same value, 1, and so they are called equivalent fractions. Equivalent fractions are fractions that have the same value.

Let’s think of pizzas this time. Figure 2 shows two images: a single pizza on the left, cut into two equal pieces, and a second pizza of the same size, cut into eight pieces on the right. This is a way to show that 12 is equivalent to 48. In other words, they are equivalent fractions.

A circle is shown that is divided into eight equal wedges by lines. The left side of the circle is a pizza with four sections making up the pizza slices. The right side has four shaded sections. Below the diagram is the fraction four eighths.
Since the same amount is of each pizza is shaded, we see that 12 is equivalent to 48. They are equivalent fractions.

How can we use mathematics to change 12 into 48? How could we take a pizza that is cut into 2 pieces and cut it into 8 pieces? We could cut each of the 2 larger pieces into 4 smaller pieces! The whole pizza would then be cut into 8 pieces instead of just 2. Mathematically, what we’ve described could be written like this as 1·42·4=48. See Figure 3.

A circle is shown and is divided in half by a vertical black line. It is further divided into eighths by the addition of dotted red lines.
Cutting each half of the pizza into 4 pieces, gives us pizza cut into 8 pieces: 1·42·4=48.

This model leads to the following property:

If we had cut the pizza differently, we could get

An image shows three rows of fractions. In the first row are the fractions “1, times 2, divided by 2, times 2, equals two fourths”. Next to this is the word “so” and the fraction “one half, equals two fourths. The second row reads “1, times 3, divided by 2 times 3, equals three sixths”. Next to this is the word “so” and the fraction “one half equals, three sixths”. The third row reads “1 times 10, divided by 2 times 10, ten twentieths”. Next to this is the word “so” and the fraction “one half equals, ten twentieths”.

So, we say 12,24,36,and1020 are equivalent fractions.

Find three fractions equivalent to 25.

Solution

Solution

To find a fraction equivalent to 25, we multiply the numerator and denominator by the same number. We can choose any number, except for zero. Let’s multiply them by 2, 3, and then 5.
A row of fractions reads “2 times 2, divided by 5 times 2, equals four tenths”. Next to this is “2, times 3, divided by 5 times 3, equals six fifteenths”. Next to this is “2 times 5, divided by 5 times 5, equals ten twenty-fifths”.
So, 410,615,and1025 are equivalent to 25.

Simplify Fractions

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

For example,

  • 23 is simplified because there are no common factors of 2 and 3.
  • 1015 is not simplified because 5 is a common factor of 10 and 15.

The phrase reduce a fraction means to simplify the fraction. 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.

In Example 1, we used the equivalent fractions property to find equivalent fractions. Now we’ll use the equivalent fractions property in reverse to simplify fractions. We can rewrite the property to show both forms together.

Simplify: 3256.

Solution

Solution

3256
Rewrite the numerator and denominator showing the common factors. A mathematical fraction displaying negative (4 multiplied by 8) over (7 multiplied by 8), with the common factor '8' highlighted in red in both numerator and denominator.
Simplify using the equivalent fractions property. 47

Notice that the fraction 47 is simplified because there are no more common factors.

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.

How to Simplify a Fraction

Simplify: 210385.

Solution

Solution

A table is shown with three columns and three rows. The first row of the left column reads “Step 1. Rewrite the numerator and denominator to show the common factors. If needed, use a factor tree”. Next to this in the middle column, it reads “rewrite 210 and 285 as the product of the primes. Next to this in the right column, it reads “negative 210 divided by 385.” Under this, is the equation “two times three times five times seven.” The five and 7 are blue and red respectively. The next row down reads “Step 2. Simplify using the equivalent fractions property by dividing out common factors.” Next to this in the middle column, it reads, “Mark the common factors 5 and 7.” Next to this in the right column, it has the equation 2 times, three times five, times seven over 5 times seven times 11. Both the 5 and the 7 are crossed out as common factors. Under this is the equation “negative two times 3 divided by 11.” The next row reads, “Step 3. Multiply the remaining factors, if necessary.” Next to this in the right column is negative six elevenths.

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

Simplify: 5x5y.

Solution

Solution

5x5y
Rewrite showing the common factors, then divide out the common factors. The image illustrates the simplification of the fraction 5x/5y. It shows how to rewrite the expression to identify common factors (5), divide them out, and then simplify to x/y.
Simplify. xy

Multiply Fractions

Many people find multiplying and dividing fractions easier than adding and subtracting fractions. So we will start with fraction multiplication.

We’ll use a model to show you how to multiply two fractions and to help you remember the procedure. Let’s start with 34.

A rectangle made up of four squares in a row. The first three squares are shaded.

Now we’ll take 12 of 34.

A rectangle made up of four squares in a row. The first three squares are shaded. The bottom halves of the first three squares are shaded darker with diagonal lines.

Notice that now, the whole is divided into 8 equal parts. So 12·34=38.

To multiply fractions, we 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 5, we will multiply negative and a positive, so the product will be negative.

Multiply: 1112·57.

Solution

Solution

The first step is to find the sign of the product. Since the signs are the different, the product is negative.

This table illustrates the step-by-step process of multiplying two fractions, showing each mathematical operation and the resulting expression.
1112·57
Determine the sign of the product; multiply. 11·512·7
Are there any common factors in the numerator and the demoninator? No. 5584

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 a1. So, for example, 3=31.

Multiply: 125(−20x).

Solution

Solution

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

125(−20x)
Write 20x as a fraction. 125(20x1)
Multiply.
Rewrite 20 to show the common factor 5 and divide it out. A mathematical expression showing the fraction (12 * 4 * 5x) divided by (5 * 1), with the '5' in the numerator and denominator canceled out.
Simplify. 48x

Divide Fractions

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 23 is 32.

Notice that 23·32=1. A number and its reciprocal multiply to 1.

To get a product of positive 1 when multiplying two numbers, the numbers must have the same sign. So reciprocals must have the same sign.

The reciprocal of 107 is 710, since 107(710)=1.

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

We need to say b0,c0andd0 to be sure we don’t divide by zero!

Divide: 23÷n5.

Solution

Solution

Step-by-step guide on dividing a numerical fraction by an algebraic fraction using the reciprocal method.
23÷n5
To divide, multiply the first fraction by the reciprocal of the second. 23·5n
Multiply. 103n

Find the quotient: 718÷(1427).

Solution

Solution

718÷(1427)
To divide, multiply the first fraction by the reciprocal of the second. 7182714
Determine the sign of the product, and then multiply.. 7271814
Rewrite showing common factors. A mathematical fraction is shown where common factors (7 and 9) in the numerator (7*9*3) and denominator (9*2*7*2) are crossed out, indicating cancellation to simplify the expression. The remaining terms are 3 in the numerator and 2*2 in the denominator.
Remove common factors. 322
Simplify. 34

There are several ways to remember which steps to take to multiply or divide fractions. One way is to repeat the call outs to yourself. If you do this each time you do an exercise, you will have the steps memorized.

  • “To multiply fractions, multiply the numerators and multiply the denominators.”
  • “To divide fractions, multiply the first fraction by the reciprocal of the second.”

Another way is to keep two examples in mind:

This is an image with two columns. The first column reads “One fourth of two pizzas is one half of a pizza. Below this are two pizzas side-by-side with a line down the center of each one representing one half. The halves are labeled “one half”. Under this is the equation “2 times 1 fourth”. Under this is another equation “two over 1 times 1 fourth.” Under this is the fraction two fourths and under this is the fraction one half. The next column reads “there are eight quarters in two dollars.” Under this are eight quarters in two rows of four. Under this is the fraction equation 2 divided by one fourth. Under this is the equation “two over one divided by one fourth.” Under this is two over one times four over one. Under this is the answer “8”.

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.

Some examples of complex fractions are:

6733458x256

To simplify a complex fraction, we remember that the fraction bar means division. For example, the complex fraction 3458 means 34÷58.

Simplify: 3458.

Solution

Solution

3458
Rewrite as division. 34÷58
Multiply the first fraction by the reciprocal of the second. 3485
Multiply. 3845
Look for common factors. An example of fraction simplification, where the common factor '4' is canceled from both the numerator and denominator of (3*4*2)/(4*5).
Divide out common factors and simplify. 65

Simplify: x2xy6.

Solution

Solution

x2xy6
Rewrite as division. x2÷xy6
Multiply the first fraction by the reciprocal of the second. x26xy
Multiply. x62xy
Look for common factors. Simplifying a fraction by canceling out common variables 'x' and 'z' from the numerator and denominator, resulting in 3 over y.
Divide out common factors and simplify. 3y

Simplify Expressions with a Fraction Bar

The line that separates the numerator from the denominator in a fraction is called a fraction bar. A fraction bar acts as grouping symbol. The order of operations then tells us to simplify the numerator and then the denominator. Then we divide.

To simplify the expression 537+1, we first simplify the numerator and the denominator separately. Then we divide.

537+1
28
14

Simplify: 42(3)22+2.

Solution

Solution

Step-by-step simplification of a mathematical expression using the order of operations.
42(3)22+2
Use the order of operations to simpliy the numerator and the denominator. 464+2
Simplify the numerator and the denominator. −26
Simplify. A negative divided by a positive is negative. 13

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.

−13=13negativepositive=negative1−3=13positivenegative=negative

Simplify: 4(−3)+6(−2)−3(2)2.

Solution

Solution

This table demonstrates the step-by-step simplification of a complex rational expression involving integer arithmetic.
4(−3)+6(−2)−3(2)2
Multiply. −12+(−12)−62
Simplify. −24−8
Divide. 3

Translate Phrases to Expressions with Fractions

Now that we have done some work with fractions, we are ready to translate phrases that would result in expressions with fractions.

The English words quotient and ratio are often used to describe fractions. Remember that “quotient” means division. The quotient of a and b is the result we get from dividing a by b, or ab.

Translate the English phrase into an algebraic expression: the quotient of the difference of m and n, and p.

Solution

Solution

We are looking for the quotient of the difference of m and n, and p. This means we want to divide the difference of mandnbyp.

mnp

Key Concepts

  • Equivalent Fractions Property: If a,b,c are numbers where b0,c0, then
    ab=a·cb·c and a·cb·c=ab.
  • Fraction Division: If a,b,candd are numbers where b0,c0,andd0, then ab÷cd=ab·dc. To divide fractions, multiply the first fraction by the reciprocal of the second.
  • Fraction Multiplication: If a,b,candd are numbers where b0,andd0, then ab·cd=acbd. To multiply fractions, multiply the numerators and multiply the denominators.
  • Placement of Negative Sign in a Fraction: For any positive numbers aandb, ab=ab=ab.
  • Property of One: aa=1; Any number, except zero, divided by itself is one.
  • 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.
  • Simplify an Expression with a Fraction Bar
    1. Simplify the expression in the numerator. Simplify the expression in the denominator.
    2. Simplify the fraction.

Practice Makes Perfect

Find Equivalent Fractions

In the following exercises, find three fractions equivalent to the given fraction. Show your work, using figures or algebra.

38

Solution

616,924,1232 answers may vary

58

59

Solution

1018,1527,2036 answers may vary

18

Simplify Fractions

In the following exercises, simplify.

4088

Solution

511

6399

10863

Solution

127

10448

120252

Solution

1021

182294

3x12y

Solution

x4y

4x32y

14x221y

Solution

2x23y

24a32b2

Multiply Fractions

In the following exercises, multiply.

34·910

Solution

2740

45·27

23(38)

Solution

14

34(49)

59·310

Solution

16

38·415

(1415)(920)

Solution

2150

(910)(2533)

(6384)(4490)

Solution

1130

(3360)(4088)

4·511

Solution

2011

5·83

37·21n

Solution

9n

56·30m

−8(174)

Solution

−34

(−1)(67)

Divide Fractions

In the following exercises, divide.

34÷23

Solution

98

45÷34

79÷(74)

Solution

49

56÷(56)

34÷x11

Solution

334x

25÷y9

518÷(1524)

Solution

49

718÷(1427)

8u15÷12v25

Solution

10u9v

12r25÷18s35

−5÷12

Solution

−10

−3÷14

34÷(−12)

Solution

116

−15÷(53)

In the following exercises, simplify.

8211235

Solution

109

9163340

452

Solution

25

5310

m3n2

Solution

2m3n

38y12

Simplify Expressions Written with a Fraction Bar

In the following exercises, simplify.

22+310

Solution

52

1946

482415

Solution

163

464+4

−6+68+4

Solution

0

−6+3178

4·36·6

Solution

13

6·69·2

42125

Solution

35

72+160

8·3+2·914+3

Solution

2817

9·64·722+3

5·63·44·52·3

Solution

97

8·97·65·69·2

523235

Solution

−8

624246

7·42(85)9·33·5

Solution

116

9·73(128)8·76·6

9(82)3(157)6(71)3(179)

Solution

52

8(92)4(149)7(83)3(169)

Translate Phrases to Expressions with Fractions

In the following exercises, translate each English phrase into an algebraic expression.

the quotient of r and the sum of s and 10

Solution

rs+10

the quotient of A and the difference of 3 and B

the quotient of the difference of xandy,and3

Solution

xy−3

the quotient of the sum of mandn,and4q

Everyday Math

Baking. A recipe for chocolate chip cookies calls for 34 cup brown sugar. Imelda wants to double the recipe. How much brown sugar will Imelda need? Show your calculation. Measuring cups usually come in sets of 14,13,12,and1 cup. Draw a diagram to show two different ways that Imelda could measure the brown sugar needed to double the cookie recipe.

Solution

(2)(34);32 cups answers will vary

Baking. Nina is making 4 pans of fudge to serve after a music recital. For each pan, she needs 23 cup of condensed milk. How much condensed milk will Nina need? Show your calculation. Measuring cups usually come in sets of 14,13,12,and1 cup. Draw a diagram to show two different ways that Nina could measure the condensed milk needed for 4 pans of fudge.

Portions Don purchased a bulk package of candy that weighs 5 pounds. He wants to sell the candy in little bags that hold 14 pound. How many little bags of candy can he fill from the bulk package?

Solution

20 bags

Portions Kristen has 34 yards of ribbon that she wants to cut into 6 equal parts to make hair ribbons for her daughter’s 6 dolls. How long will each doll’s hair ribbon be?

Writing Exercises

Rafael wanted to order half a medium pizza at a restaurant. The waiter told him that a medium pizza could be cut into 6 or 8 slices. Would he prefer 3 out of 6 slices or 4 out of 8 slices? Rafael replied that since he wasn’t very hungry, he would prefer 3 out of 6 slices. Explain what is wrong with Rafael’s reasoning.

Solution

Answers may vary

Give an example from everyday life that demonstrates how 12·23is13.

Explain how you find the reciprocal of a fraction.

Solution

Answers may 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.

A table is shown that is made up of four columns and seven rows. The first row reads “I can…” in the first column, “Confidently” in the second column, “With some help” in the third column and “No – I don’t get it” in the last column. The next row down in the first column reads “find equivalent fractions”, under this reads “simplify fractions”, under this reads “multiply fractions”, under this reads “divide fractions”, under this reads “Simplify expressions written with a fraction bar” and under this reads “translate phrases to expressions with fractions.”

After looking at the checklist, do you think you are well prepared for the next section? Why or why not?

complex fraction
A complex fraction is a fraction in which the numerator or the denominator contains a fraction.
denominator
The denominator is the value on the bottom part of the fraction that indicates the number of equal parts into which the whole has been divided.
equivalent fractions
Equivalent fractions are fractions that have the same value.
fraction
A fraction is written ab, where b0 a is the numerator and b is the denominator. A fraction represents parts of a whole. The denominator b is the number of equal parts the whole has been divided into, and the numerator a indicates how many parts are included.
numerator
The numerator is the value on the top part of the fraction that indicates how many parts of the whole are included.
reciprocal
The reciprocal of ab is ba. A number and its reciprocal multiply to one: ab·ba=1.
simplified fraction
A fraction is considered simplified if there are no common factors in its numerator and denominator.