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学習ガイド > Prealgebra

Applications of the Subtraction and Addition Properties

Learning Outcomes

  • Translate a sentence into an algebraic equation
  • Solve an equation that has been translated and verify the solution is correct
  • Solve an application problem by writing and solving an algebraic equation
  In previous chapters, we translated word sentences into equations. This skill will help you when you solve word problems. Previously, you translated phrases into expressions, and now we will translate phrases into mathematical equations so we can solve them. The first step in translating phrases into equations is to look for the word (or words) that translate(s) to the equal sign. The table below reminds us of some of the words that translate to the equal sign.
Equals (=)
is is equal to is the same as the result is gives was will be
Let’s review the steps we used to translate a sentence into an equation.
Translate a word sentence to an algebraic equation.
  1. Locate the "equals" word(s). Translate to an equal sign.
  2. Translate the words to the left of the "equals" word(s) into an algebraic expression.
  3. Translate the words to the right of the "equals" word(s) into an algebraic expression.
  In our first example we will translate and solve a one-step equation.

Example

Translate and solve: five more than xx is equal to 2626. Solution:
Translate. Five more than xx   ⇒x+5\Rightarrow\quad{x+5} is equal to   ⇒=\Rightarrow\quad{=} 26[/latex] [latex]⇒2626[/latex]   [latex]\Rightarrow\quad{26} x+5=26x+5=26
Subtract 5 from both sides. x+5−5=26−5x+5\color{red}{-5}=26\color{red}{-5}
Simplify. x=21x=21
Check: Is 2626 five more than 2121 ? 21+5=?2621+5\stackrel{\text{?}}{=}26 26=26✓26=26\quad\checkmark The solution checks.
   

Example

Translate and solve: The difference of 5p5p and 4p4p is 2323.

Answer:

Solution:
Translate. The difference of 5p5p and 4p4p   ⇒5p−4p\Rightarrow\quad{5p-4p} is   ⇒=\Rightarrow\quad{=} 23[/latex] [latex]⇒2323[/latex]   [latex]\Rightarrow\quad{23} 5p−4p=235p-4p=23
Simplify. p=23p=23
Check: 5p−4p=235p-4p=23 5(23)−4(23)=?235(23)-4(23)\stackrel{?}{=}23 115−92=?23115-92\stackrel{?}{=}23 23=23✓23=23\quad\checkmark
The solution checks.

    Watch this video for more examples of how to translate a phrase into an equation, then solve it. https://youtu.be/w-64WyZYAMU

Translate and Solve Applications

In most of the application problems we solved earlier, we were able to find the quantity we were looking for by simplifying an algebraic expression. Now we will be using equations to solve application problems. We’ll start by restating the problem in just one sentence, then we'll assign a variable, and then we'll translate the sentence into an equation to solve. When assigning a variable, choose a letter that reminds you of what you are looking for.

Example

The Robles family has two dogs, Buster and Chandler. Together, they weigh 7171 pounds. Chandler weighs 2828 pounds. How much does Buster weigh?

Answer:

Solution:
Read the problem carefully.
Identify what you are asked to find, and choose a variable to represent it. How much does Buster weigh? Let b=b= Buster's weight
Write a sentence that gives the information to find it. Buster's weight plus Chandler's weight equals 71 pounds.
We will restate the problem, and then include the given information. Buster's weight plus 28 equals 71.
Translate the sentence into an equation, using the variable bb. b+28=71b+28=71
Solve the equation using good algebraic techniques. b+28−28=71−28b+28-28=71-28 b=43b=43
Check the answer in the problem and make sure it makes sense.
Is 43 pounds a reasonable weight for a dog?  Yes.
Does Buster's weight plus Chandler's weight equal 71 pounds?  43+28=?7143+28\stackrel{?}{=}71
 71=71✓71=71\quad\checkmark
Write a complete sentence that answers the question, "How much does Buster weigh?" Buster weighs 4343 pounds.

   

Devise a problem-solving strategy.

  1. Read the problem. Make sure you understand all the words and ideas.
  2. Identify what you are looking for.
  3. Name what you are looking for. Choose a variable to represent that quantity.
  4. Translate into an equation. It may be helpful to restate the problem in one sentence with all the important information. Then, translate the English sentence into an algebra equation.
  5. Solve the equation using good algebra techniques.
  6. Check the answer in the problem and make sure it makes sense.
  7. Answer the question with a complete sentence.
  Let's take a look at the problem-solving strategy in action.

example

Shayla paid $24,57524,575 for her new car. This was $875875 less than the sticker price. What was the sticker price of the car?

Answer:

Solution:
What are you asked to find? "What was the sticker price of the car?"
Assign a variable. Let s=s= the sticker price of the car.
Write a sentence that gives the information to find it. $24,575 is $875 less than the sticker price. $24,575 is $875 less than ss.
Translate into an equation. 24,575=s−87524,575=s-875
Solve. 24,575+875=s−875+87524,575+875=s-875+875 24,575=s24,575=s
Check: Is $875 less than $25,450 equal to $24,575? 25,450−875=?24,57525,450 - 875\stackrel{?}{=}24,575 24,575=24,575✓24,575=24,575\quad\checkmark
Write a sentence that answers the question. The sticker price was $25,45025,450.

Now you can try translating an equation from a statement that represents subtraction.   In the following video you will see another example of how to translate a phrase into an equation and solve. https://youtu.be/0eUNh_Qkw9A  

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