Money Math · Lesson Plan

Discounts and Dividing by Rational Numbers

½ off, ⅓ off, ¼ off — store signs are written as fractions, so discount math is really fraction math. This lesson reviews dividing rational numbers (invert and multiply, and putting a whole number over one), then applies it to prices: multiply the price by the fraction to get the discount, and subtract to get the sale price. Ten problems ask for both, with a full answer key.

Grades 6–9 Lesson Plan 30–45 minutes Free Lesson Plan Lesson & Worksheet: Full Membership

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

Divide two fractions by inverting the second fraction and multiplying
Divide a whole number by a fraction by writing the whole number over one
Simplify a fraction to lowest terms
Use the key word ‘of’ to multiply a price by a fraction
Find both the discount and the sale price of an item

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

Discount: An amount of money subtracted from the total cost of an item.
Rational number: A number that can be written as a fraction.
Invert: To flip a fraction — the step that turns division into multiplication.
Simplify: To reduce a fraction to lowest terms.
Of: A key word meaning multiply.
Sale price: The original price minus the discount.

For Teachers

Lesson plan

Estimated time: one 30–45 minute class period.

Lesson sequence

Introduction (5 min). Show a store sign reading “½ off.” Establish that a discount is money subtracted from the price, and that it is often written as a fraction.
Review dividing rational numbers (10 min). Work 3/8 ÷ 1/2 by inverting and multiplying, then simplify. Repeat with a whole number (24 ÷ 1/3) by writing 24 as 24/1.
Apply it to a price (10 min). “What is one-half off of $26.00?” Multiply the price by the fraction to get the $13.00 discount, then subtract to get the $13.00 sale price. Work the two-pair shoe example to show a discount applied to only one item.
Worksheet (15 min). Students find the discount and sale price for ten items.
Review (5 min). Check answers with the key; each problem has two answers, so watch for students who reported only one.

Assessment

Assess the completed worksheet against the included answer key.

Discussion

Discussion questions

Why does dividing by a fraction give a bigger answer than you might expect?
Why do you write a whole number over one before dividing by a fraction?
How is ‘½ off’ different from ‘paying ½’? (They are the same — why?)
Which is easier for ¼ off — fractions or percents?
Why does a worksheet ask for the discount and the sale price separately?

Printable Lesson, Worksheet & Answer Key