Pre-AlgebraPre-Algebra

Solve y + 5 = 13.

Solving Equations by Adding or SubtractingSolving Equations by Adding or Subtracting

Lesson 2-5

Method 1: Method 2:

y + 5 = 13 Subtract 5

y + 5 – 5 = 13 – 5 from each side.

y = 8 Simplify.

y + 5 = 13

y = 8

Check: y + 5 = 13

8 + 5 13 Replace y with 8.

13 = 13

– 5 = – 5

Additional Examples

Pre-AlgebraPre-Algebra

Larissa wants to increase the number of books in her

collection to 327 books. She has 250 books now. Find the number

of books she needs to buy.

Solving Equations by Adding or SubtractingSolving Equations by Adding or Subtracting

Lesson 2-5

target numberWords plusis 250 number to buy

= number to buy.xLet

Equation 327 + x250=

Additional Examples

Pre-AlgebraPre-Algebra

(continued)

Solving Equations by Adding or SubtractingSolving Equations by Adding or Subtracting

Lesson 2-5

327 = 250 + x

Larissa needs to buy 77 more books.

327 = x + 250 Use the Commutative Property of Addition.

327 – 250 = x + 250 – 250 Subtract 250 from each side.

77 = x Simplify.

Check:  Is the answer reasonable?250 plus the number of books bought should be a total collection of 327.

250 + 77 = 327

Additional Examples

Pre-AlgebraPre-Algebra

Solve c – 23 = – 40.

Solving Equations by Adding or SubtractingSolving Equations by Adding or Subtracting

Lesson 2-5

c – 23 = – 40

c – 23 + 23 = – 40 + 23 Add 23 to each side.

c = –17 Simplify.

Additional Examples

Pre-AlgebraPre-Algebra

Marcy’s CD player cost $115 less than her DVD player. Her

CD player cost $78. How much did her DVD player cost?

Solving Equations by Adding or SubtractingSolving Equations by Adding or Subtracting

Lesson 2-5

78 = t – 115 Write an equation.

78 + 115 = t – 115 + 115   Add 115 to each side.

193 = t Simplify.

Marcy’s DVD player cost $193.

cost of CD player $115 cost of DVD playerWords less thanwas

t = cost of the DVD player.Let

t 115Equation 78 = –

Additional Examples