Algebra 1 Common Core Student Edition, Grade 8-9

Think

What operations are

used in th e equation?

The e q u a tio n uses

multiplication and

a d d itio n. You can undo

the addition first, and

then the m ultiplication.

Think
How can a model
help you w rite the
equation?
The m odel show s th a t
a h a lf o f a sheet per ad
plus 5 sheets fo r th e
title banner is equal to
18 sheets.
I- 1 8................. 1

Solving a Two-Step Equation

What is the solution of 2x + 3 = 15?

2x + 3 = 15

Subtract 3 from each side.

Simplify.

Divide each side by 2.

Simplify.

2x + 3 - 3 = 15

2x = 12

2 x

2

12

2

x = 6

Check 2x + 3 = 15

2(6) + 3 = 15

15 = 15

Substitute 6 for x.

Simplify. The solution checks.

^ Got It? 1.W hat is th e solution of 5 = ; 3?

Problem 2 Using an Equation as a M odel

Community Service You are making a bulletin board to advertise community

service opportunities in your town. You plan to use half a sheet of construction

paper for each ad. You need 5 sheets of construction paper for a title banner.

You have 18 sheets of construction paper. How many ads can you make?

• Paper per ad: j sheet


• Paper for banner: 5 sheets


• Total paper: 18 sheets

Need

The num ber o f ads

you can make

F*

W rite and solve an e q u a tio n. Let th e

variable represent the unknown.

Let a = th e n u m b e r of ads you can make.

\a + 5 = 18

\a + 5 - 5 = 18

= 13

Subtract 5 from each side.

Simplify.

Multiply each side by 2.

Simplify.

You can m ake 26 com m unity service advertisem ents for the bulletin board.

2 L a 2(13)

a = 26

G ot It? 2. Suppose you u sed o n e q u a rte r of a sh eet of p a p e r for each ad an d

four full sheets for th e title b a n n e r in Problem 2. How m any ads

could you make?

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Lesson 2-2 So l v i n g Tw o - St e p Eq u a t i o n s -