A bar diagram helps solve a two-step equation problem by visually representing the quantities and their relationships. The bar diagram shows the total number of postcards Miranda bought and the total cost. It can be used to write an equation relating the unknown cost of a large postcard to the total quantity and cost. Solving this equation reveals that the cost of one large postcard is $2.50.

1. HOW does a bar diagram
help you solve a real-
world problem involving a
two-step equation?
Course 3, Inquiry Lab before Lesson 2-2
Expressions and Equations

2. • 8.EE.7
Solve linear equations in one variable.
• 8.EE.7a
Give examples of linear equations in one variable with one solution, infinitely many
solutions, or no solutions. Show which of these possibilities is the case by
successively transforming the given equation into simpler forms, until an equivalent
equation of the form x = a, a = a, or a = b results (where a and b are different
numbers).
Mathematical Practices
1 Make sense of problems and persevere in solving them.
2 Construct viable arguments and critique the reasoning of others.
3 Construct viable arguments and critique the reasoning of others.
4 Model with mathematics.
Course 3, Inquiry Lab before Lesson 2-2 Common Core State Standards © Copyright 2010. National Governors Association Center for Best
Practices and Council of Chief State School Officers. All rights reserved.
Expressions and Equations

3. Course 3, Inquiry Lab before Lesson 2-2
Activity
continued

Expressions and Equations
Miranda bought two large postcards and four small postcards at a
souvenir shop. Each small postcard costs $0.50. If Miranda spent
$5.00 on postcards, what is the cost of one large postcard?
The bar diagram represents the total number of postcards
and the total cost. Label the missing parts.

4. Course 3, Inquiry Lab before Lesson 2-2
Activity
continued

Expressions and Equations
Miranda bought two large postcards and four small postcards at a
souvenir shop. Each small postcard costs $0.50. If Miranda spent
$5.00 on postcards, what is the cost of one large postcard?
Fill in the boxes to write an equation that represents the
bar diagram. The cost of a large postcard is the
unknown, so it is represented by the variable p.
2p + =

5. Course 3, Inquiry Lab before Lesson 2-2
Expressions and Equations
Miranda bought two large postcards and four small postcards at a
souvenir shop. Each small postcard costs $0.50. If Miranda spent
$5.00 on postcards, what is the cost of one large postcard?
Find the cost of the large postcards by working backward.
The cost of one large postcard is __________________________.

6. Course 3, Inquiry Lab before Lesson 2-2
HOW does a bar diagram
help you solve a real-
world problem involving
a two-step equation?
Expressions and Equations