Solving Addition and Subtraction Equations

Solving Addition and Subtraction Equations

How can you get the variable alone in an addition or a subtraction equation?

When solving addition and subtraction equations, there are two ideas that need to be involved...

• 1. There needs to be an inverse relationship.

• 2. Property of equality

Inverse Relationship

• Addition undergoes subtraction.

• Subtraction undergoes addition.

Property of Equality

The same value can be added to or subtracted from both sides of an equation, and equality is maintained.

How can you get the variable alone in a subtraction equation?

x - 19 = 34

x - 19 = 34

• Adding 19 is the inverse of subtracting 19.

• SOLVE: x - 19 = 34

• SOLVE: x - 19 + 19 = 34 + 19 --> Adding 19 will undo subtracting 19. That will leave x alone.

• SOLVE: x = 34 + 19

• SOLVE: x = 53

Checking Our Work:

Equation: x - 19 = 34

• To check, substitute 53 for x in you equation.

• x - 19 = 34

• 53 - 19 = 34

• 34 = 34 --> It checks

How can you get the variable alone in a addition equation?

x + 19 = 34

x + 19 = 34

• Subtracting 19 is the inverse of adding 19.

• SOLVE: x + 19 = 34

• SOLVE: x + 19 - 19 = 34 - 19 --> Subtracting 19 will undo adding 19. That will leave x alone.

• SOLVE: x = 34 - 19

• SOLVE: x = 15

Checking Our Work:

Equation: x + 19 = 34

• To check, substitute 15 for x in you equation.

• x + 19 = 34

• 15 + 19 = 34

• 34 = 34 --> It checks

Now It Is Your Turn!

Remember to use the inverse relationship and the property of equality.

Fill in the Blanks

Explain how to get the variable alone in the equation.

25 + m = 49

Fill in the Blanks

Solve the equation.

12 = x - 11

Fill in the Blanks

Explain how to get the variable alone in the equation.

y - 12 = 89

Y - 12 +

= 89 + 12

Fill in the Blanks

Complete solving the equation.

20 = y + 12

20 - 12 = y + 12 - 12

Fill in the Blanks

Solve the equation.

55 = x - 48

Poll

14. How do you feel on evaluating equations?

• Great!

• So-So.

• Confused?