INSTRUCTORS Carleen Eaton Grant Fraser Eric Smith

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For more information, please see full course syllabus of Algebra 1

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### Addition and Subtraction Techniques

• Solving an equation means finding all values of the variable that make the equation true.
• To solve an equation, isolate the variable on one side of the equation and with a coefficient of 1.
• You can do this by using the addition and subtraction properties of equality: If you add or subtract the same quantity to both sides of an equation, the resulting equation has the same solutions as the original equation.

### Addition and Subtraction Techniques

40 + x = - 22
• 40 + x - 40 = - 22 - 40
x = - 64
10 = 54 - y
• 10 - 54 = 54 - y - 54
• - 44 = - y
44 = y
r − [1/5] = [2/5]
• r − [1/5] + [1/5] = [2/5] + [1/5]
r = [3/5]
[5/8] = [2/8] − t
• [5/8] − [2/8] = [2/8] − t − [2/8]
• [3/8] = − t
− [3/8] = t
Thirty - five is six more than a number. Find the number.
x = unknown number
• 35 = 6 + x
• 35 - 6 = 6 + x - 6
29 = x
Twelve less than a number is sixty six. Find the number.
n = unknown number
• n - 12 = 66
• n - 12 + 12 = 66 + 12
n = 78
Eighteen is thirty - two less than a number. Find the number.
n = unknown number
• 18 = n - 32
• 18 + 32 = n - 32 + 32
50 = n
The sum of 6, 8, and a number is equal to 30. What is the number?
x = unknown number
• 6 + 8 + x = 30
• 14 + x = 30
• 14 + x - 14 = 30 - 14
x = 16
The difference of 55 and a number is equal to 23. What is the number?
x = unknown number
• 55 - x = 23
• 55 - x - 55 = 23 - 55
• - x = - 32
x = 32
The sum of 21.8, 60.1 and a number is equal to 111.5. What is the number?
x = unknown number
• 21.8 + 60.1 + x = 111.5
• 81.9 + x = 111.5
• 81.9 + x - 81.9 = 111.5 - 81.9
x = 29.6

*These practice questions are only helpful when you work on them offline on a piece of paper and then use the solution steps function to check your answer.

### Addition and Subtraction Techniques

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

• Intro 0:00
• Techniques 0:21