Money Math · Lesson Plan

Calculating an Original Price

Working backward: if you know a discount amount and its percent, what was the original price? This lesson teaches the ‘is/of’ set-up — ’18 is 40% of what number?’ becomes 18 = .40x — then divide to solve for the original price. Students practice on thirteen problems, including a real shopping scenario (answer key included).

Grades 6–9 Lesson Plan 30–45 minutes Free Lesson

Calculating an original price lesson illustration

For Teachers

Lesson at a glance

Topic: Money Math
Grade Level: Grades 6–9
Resource Type: Lesson + Worksheet
Estimated Time: 30–45 minutes
Format: Lesson + worksheet + answer key
Materials: Printable lesson, worksheet, answer key, calculator

What Students Learn

Learning objectives

Recognize when you are solving for the original price
Translate ‘X is P% of what number’ into an equation
Convert the percent to a decimal
Divide to solve for the unknown original amount
Apply the method to a real shopping scenario

Materials

What you’ll need

Printed copies of the lesson and worksheet (one per student)
Calculators
Pencils
Whiteboard or projector for worked examples

Key Terms

Vocabulary

Original price: The price before the discount — the unknown here.
Discount amount: The dollars taken off.
Percent: The portion of the original that the discount represents.
Equation: A statement set equal that you solve for the unknown.
Variable: The letter (x) standing for the original price.
Divide: The step that isolates the variable.

For Teachers

Lesson plan

Estimated time: one 30–45 minute class period.

Lesson sequence

Introduction (5 min). Pose “$18 is 40% of what number?” and connect it to finding an original price.
Teach the method (12 min). Translate to 18 = .40x, divide both sides by .40, and interpret the answer as money. Work the skateboard example.
Worksheet (15 min). Students solve thirteen problems, including a shopping scenario.
Review (8 min). Check answers with the key.

Assessment

Assess the completed worksheet against the included answer key.

Discussion

Discussion questions

How do you know you’re solving for the original price?
How does ‘X is P% of what number’ become an equation?
Why do you divide to find the unknown?
How is this the reverse of finding a discount amount?
Where might working backward to an original price be useful?

Printable Lesson, Worksheet & Answer Key