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2. Solving One-Step Equations with Rational Coefficients
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Chapter 6
2. 

Solving One-Step Equations with Rational Coefficients

This lesson explores the methods for solving one-step equations where the coefficients are rational numbers. It emphasizes the importance of using the Multiplication Property of Equality and the Division Property of Equality to find the solution. These techniques are not just theoretical; they have practical applications too. For example, they can be used in financial calculations, engineering problems, and various other fields that require precise mathematical reasoning. The goal is to make learners proficient in solving such equations, whether they are high school students preparing for advanced algebra or professionals needing these skills for their work.

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Student Learning Objectives:
  • Use the Addition and Subtraction Properties of Equality to create equivalent equations and solve equations
  • Solve equations with rational coefficients
12 Theory slides
11 Exercises - Grade E - A
Each lesson is meant to take 1-2 classroom sessions
Solving One-Step Equations with Rational Coefficients
Slide of 12
Equations can include variables multiplied or divided by rational numbers. To solve these equations, we multiply or divide both sides by the same number. This lesson explains how to solve these equations and use them to model real-life situations.

Catch-Up and Review

Here are a few recommended readings before getting started with this lesson.

Challenge

A Vinyl Record Collection

Kriz has a collection of 200 vinyl records.


They bought 10 records each month while building the collection.

a

Write an equation in terms of m that represents the situation.

b

Solve the equation to find how long it took Kriz to build their collection.

Discussion

Multiplication Property of Equality

Multiplication and division are inverse operations. They can be used to solve equations using the following Properties of Equality.

Rule

Multiplication Property of Equality

Given an equation, multiplying each side of the equation by the same number results in an equivalent equation. Let a, b, and c be real numbers.

If a = b, then a * c = b * c.

The Multiplication Property of Equality is an axiom, so it is accepted without proof. This property is one of the Properties of Equality that can be used when solving equations. Consider the following example. x÷4&=2 x÷4 * 4&=2 * 4 x&=8

Multiplying both sides of the equation by 4 isolates the variable x and allows us to find the solution of the equation.
Discussion

Division Property of Equality

Dividing each side of an equation by the same nonzero number results in an equivalent equation. Let a, b, and c be real numbers.

If a = b and c≠ 0, then a ÷ c = b ÷ c.

The Division Property of Equality is an axiom, so it is accepted without proof. This property is one of the Properties of Equality that can be used when solving equations. 5x&=10 5x ÷ 5&=10 ÷ 5 x&=2

Dividing both sides of the equation by 5 isolates the variable x and allows us to find the solution of the equation.
Example

Bakery Orders

a

A baker packs cookies into 5 boxes. Each box contains the same number of cookies. There are a total of 180 cookies. This situation can be represented by an equation.

5b = 180 Here, b represents the number of cookies in one box. Solve the equation to find the number of cookies b in each box.

b

The baker is also packing a cupcake order. The baker wants to pack the cupcakes into 5 boxes as well. Each box will contain 6 cupcakes. The following equation represents this situation.

c/5 = 6 Solve this equation to find the total number of cupcakes c in the order.

Solution

a

Let's consider the given equation.

5b = 180 We can solve it by isolating the variable b on one side of the equation using inverse operations. Since b is multiplied by 5, let's divide each side by 5 using the Division Property of Equality.

5b=180
5b/5 = 180/5
5b/5 = 180/5
b = 180/5
b = 36

Therefore, since b is the number of cookies in each box, each box contains 36 cookies. Let's also check our answer by substituting 36 for b in the equation and simplifying.

5b = 180
5( 36) ? = 180
180 = 180 ✓

We got Substituting 36 for b into the equation results in a true statement, so b = 36 is the correct solution.

b

Let's consider the given equation.

c/5 = 6 Here, the variable c is divided by 5. To isolate it, we will multiply each side of the equation by 5 using the Multiplication Property of Equality.

c/5 = 6
c/5 * 5 = 6* 5
c = 6* 5
c = 30

Therefore, since c represents the number cupcakes in the order, there are 30 cupcakes in the order. Let's substitute 30 for c in the equation to check our answer.

c/5 = 6
30/5 ? = 6
6 = 6 ✓

Substituting 30 for c into the equation results in a true statement. This means that c = 30 is the correct solution.

Discussion

Solving Equations With Rational Coefficients

The Multiplication Property of Equality can be used instead of the Division Property of Equality when solving an equation with a rational coefficient. Consider an equation in the form abx = c. 3/5x = 6 The coefficient 35 is a fraction. The equation can be solved by multiplying both sides by the reciprocal of 35. The reciprocal of 35 is 53, so multiply both sides by 53.

3/5x = 6
3/5x * 5/3 = 6 * 5/3
▼
Simplify
x * 3/5 * 5/3 = 6 * 5/3
x * 1 = 6 * 5/3
x = 6* 5/3
x = 6* 5/3
x = 30/3
x = 10
Example

Vinyl Records, Rotations, and Song Length

A record rotates 190 times while playing a song on the album. It rotates 59 of a full rotation every second that it plays.

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This situation can be represented by the following equation. 5/9t = 190 In this equation, t represents the length of the song in seconds. Solve the equation to find the length of the song.

Hint

Identify the coefficient of the variable. Multiply both sides of the equation by the reciprocal of the coefficient.

Solution

Let's consider the given equation. 5/9 t = 190 Here, the variable is t and its coefficient is the fraction 59. We can isolate the variable by multiplying both sides of the equation by 95, the reciprocal of 59. Let's do it!

5/9t = 190
5/9t*9/5= 190*9/5
▼
Simplify
t* 5/9*9/5= 190*9/5
t* 1= 190*9/5
t = 190*9/5
t = 190*9/5
t = 1710/5
t = 342

The solution to the equation is t = 342, which means that the song is 342 seconds long.

Pop Quiz

Solving Equations

Solve the equations using the Multiplication Property of Equality or the Division Property of Equality. If necessary, round the answer to two decimal places.

Solve the equation
Discussion

Writing Equations

Many real-life situations can be algebraically modeled by equations. These equations usually involve a variable that represents an unknown quantity. Consider modeling the following situation.

Diego categorizes his father's book collection by genre. He finds out that there are 8 different genres, each with the same number of books. The collection contains 216 books. How many books are there in each genre?

This situation can be described in one sentence as follows. The product of the number of genres and the number of books in each genre is equal to the total number of books. The unknown quantity is the number of books in each genre. Let x be the variable representing this unknown quantity. Then, the verbal sentence can be translated into an algebraic equation. The product of the number of genres and the number of books in each genre is equal to the total number of books. ⇓ 8 * x = 200 The equation can now be solved to find the number x of books in each genre. Use the Division Property of Equality.

8x = 216
8x/8 = 216/8
8x/8 = 216/8
x = 216/8
x=27

Since x represents the number of books in each genre, we can conclude that in Diego's father's collection, there are 27 books in each genre.
Example

Earning Money for a Game System

Maya earns money as a dog walker. She wants to earn $600 for a new video game system. Her neighbor offers her $12 per walk to walk his dog.

a

Write an equation for the number x of times Maya has to walk her neighbor's dog to earn enough money to buy the game system.

b

Solve the equation.

c

Which of the following is a true statement?

Hint

a

Assign the variable to the unknown quantity.

b

Use the Properties of Equality to solve the equation written in Part A.

c

What does the variable represent?

Solution

a

We know that Maya gets $ 12 each time she walks the dog. She will get $ 12 x after x walks and she wants these earnings to equal $ 600. The following equation models this situation.

12 x = 600

b

Let's solve the equation we wrote in Part A.

12x = 600 We will isolate x on one side of the equation using inverse operations. Since x is multiplied by 12, let's divide each side by 12 using the Division Property of Equality.

12x = 600
12x/12 = 600/12
12x/12 = 600/12
x = 600/12
x = 50

The solution to the equation is x = 50.

c

In Part B, we found that x = 50 solves our equation. Therefore, Maya needs to walk the dog exactly 50 times.

Example

Stacking the Decks

Ignacio is sorting t trading cards into decks.


He places 60 cards in each deck and creates 3 decks.

a

Write an equation to find the total number of trading cards t that Ignacio has.

b

Solve the equation.

c

Which of the following is a true statement?

Hint

a

Assign the variable to the unknown quantity.

c

What does the variable represent?

Solution

a

Ignacio has t cards. He divides them equally into 3 decks, so each deck contains t 3 cards. Since each deck has 60 cards, we can write the following equation.

t/3 = 60 Note that multiple equivalent equations will also represent this situation. An example of such an equation is t = 3 * 60.

b

Let's solve the equation we wrote in Part A.

t/3 = 60 We will isolate t on one side of the equation using inverse operations. Since t is divided by 3, let's multiply each side by 3 using the Multiplication Property of Equality.

t/3 = 60
t/3 * 3 = 60 * 3
t = 60 * 3
t = 180

The solution to the equation is t = 180.

c

In Part B, we found that t=180 solves our equation. Therefore, Ignacio has exactly 180 trading cards, which is fewer than 200.

Closure

How Long Did It Take To Compile the Collection?

We were asked how long it took Kriz to build their record collection. We can write an equation that models the situation and solve it to find this information. Kriz bought 10 records every month until they had 200 records.

a

Write an equation in terms of m that represents the situation.

b

Solve the equation to find the time it took Kriz to gather their collection of records.

Hint

a

Assign a variable to the number of months.

Solution

a

Let m be the number of months Kriz needed to build their record collection. We know that Kriz bought 10 records every month, so, after m months, he had 10 m records. There are 200 records in the collection, so 10 m must be equal to 200.

10 m = 200

b

To solve the equation from Part A, we will isolate m on one side of the equation using inverse operations. Since m is multiplied by 10, let's divide each side by 10 using the Division Property of Equality.

10m = 200
10m/10 = 200/10
m = 200/10
m=20

The solution to the equation is m=20. This means it took 20 months to build their collection.

Extra

Equations With Decimal Coefficients
Consider an equation where the coefficient is a decimal. 1.6x = 12 Equations where the coefficient is a decimal can be solved the same way as equations with integer or fractional coefficients. In this case, this means dividing both sides of the equation by the coefficient 1.6.

1.6x = 12
1.6x/1.6 = 12/1.6
x = 12/1.6
x = 7.5



Solving One-Step Equations with Rational Coefficients
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