1. One-Step Addition and Subtraction Equations
Chapter 2 Lesson 3
Seventh Grade Math

2. Another Look at Mental Math Equations (On the number line)
x + 3 = = 2
Where do you start so that when you move
three to the right you end at 2?

3. x = -5
Think, where do you start so that when you move two to the left you end at -5?

4. Solving Equations is all about OPPOSITES!
If you want to find where you started from on the number line, you have to move in the opposite direction.
INVERSE OPERATIONS: Mathematical operations that “undo” each other
Addition/subtraction
Multiplication/division

5. Examples Using Inverse Operations
= 10
THINK: The opposite of +2 is -2
10 – 2 = 8

6. Golden Rule of Algebra Balance Scale Whatever you do to one
side of the equation,
you must do to the other!
Balance Scale

7. Properties of Equality
Addition Property of Equality
If a = b then a + c = b + c
Subtraction Property of Equality
If a = b then a - c = b - c

8. Easy Examples Using Inverse Operations to Solve One-Step Addition and Subtraction Equations
x + 5 = ) y = ) j + 11 = 60
4) x – 33 = ) y – 14 = ) j – 10 = 23

9. Kicking it up a notch… x + -2 = -6 2) y + 7 = 3 3) j + 3 = -2
Draw a line down your equal sign to make
Sure you are keeping your equation balanced.
2) Show all work (even if you can do it in your head!)
3) Watch all sign rules
4) Always use substitution to check your answer!
x = ) y + 7 = 3 3) j + 3 = -2
4) v – 5 = ) J – 3 = ) y – (-4) = 12

10. White Board Practice x + 4 = 18 x – 5 = 20 x + 1.2 = 4 x – 4.3 = 6.3
SHOW ALL WORK! Circle your solution.
x + 4 = 18
x – 5 = 20
x = 4
x – 4.3 = 6.3
y + 55 = 110
J – 30 = 53
x + 22 = 40
x – 220 = 500

11. White Board Practice With Negatives
x + -3 = 10 y + -5 = 15 j = -4 m = -12 x + 10 = -4 y + 20 = -12 s + 12 = -8 x + -9 = -21

12. White Board Practice With Negatives(sub)
x – 7 = -3 y – 11 = -15 j – 22 = -6 x – (-3) = 5 y – (-6) = 33 k – (-20) = 25 m – (-3) = -5 x – (-9) = -24

13. Error Analysis- Correct and Explain the Mistakes
1) x + 23 = ) y – (-4) = 20
= 18 The opposite of subtraction is addition
x = = 24
j – 15 = ) x = -22
The opposite of -3 is The opposite of addition is subtraction
= =
j = x = -46