Curriculum  /  Math  /  7th Grade  /  Unit 5: Percent and Scaling  /  Lesson 10

Percent and Scaling

Lesson 10

Math

Unit 5

7th Grade

Lesson 10 of 19

Objective

Solve percent applications involving simple interest, commissions, and other fees.

Common Core Standards

Core Standards

  • 7.EE.B.3 — Solve multi-step real-life and mathematical problems posed with positive and negative rational numbers in any form (whole numbers, fractions, and decimals), using tools strategically. Apply properties of operations to calculate with numbers in any form; convert between forms as appropriate; and assess the reasonableness of answers using mental computation and estimation strategies. For example: If a woman making $25 an hour gets a 10% raise, she will make an additional 1/10 of her salary an hour, or $2.50, for a new salary of $27.50. If you want to place a towel bar 9 3/4 inches long in the center of a door that is 27 1/2 inches wide, you will need to place the bar about 9 inches from each edge; this estimate can be used as a check on the exact computation.
  • 7.RP.A.3 — Use proportional relationships to solve multistep ratio and percent problems. Examples: simple interest, tax, markups and markdowns, gratuities and commissions, fees, percent increase and decrease, percent error.

Foundational Standards

  • 6.RP.A.3.C

Criteria for Success

  1. Find simple interest using the formula $${ I=PRT}$$, where I represents the simple interest, $$P$$ represents the principle amount, $$R$$ represents the interest rate, and $$T$$ represents the time of the investment.
  2. Solve percent application problems involving commissions and fees.

Tips for Teachers

In Lessons 9–11, students apply the strategies and skills they learned so far in this unit to solve real-world percent applications (MP.4). In this lesson, students look at examples involving simple interest, commission, and fees. Ensure students have an adequate working knowledge of these concepts so that they can access the problems appropriately.

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Anchor Problems

25-30 minutes

Problem 1

Larry invests $500 in a savings plan. The plan pays 4% interest each year on his $500 account balance. The table below shows the balance of his account after each year for the next 5 years. He did not make any deposits or withdrawals during this time. 

Time (in years) Balance (in dollars)
1 500
2 520
3 540
4 560
5 580

a.   How much interest did Larry earn each year? Where do you see this in the table?

b.   How is the amount of interest determined?

c.   Assuming Larry makes no additional deposits or withdrawals, how much interest will he earn after 8 years?

d.   What equation can Larry use to determine the interest he will earn on his account after $$T$$ years? 

e.   Is there a proportional relationship between the amount of interest earned and the number of years of the investment? If so, what is the constant of proportionality?

Guiding Questions

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Student Response

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References

EngageNY Mathematics Grade 7 Mathematics > Module 4 > Topic B > Lesson 10 — Example 1

Grade 7 Mathematics > Module 4 > Topic B > Lesson 10 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Modified by Fishtank Learning, Inc.

Problem 2

At a furniture store, the employees earn a 2.5% commission on every sale they make. 

a.   If Robert made $8,850 in sales one week, how much money in commission did he earn?

b.   Francesca made $279 in commission that same week, at the same rate. How much did she sell? 

Guiding Questions

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Student Response

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Problem 3

Tyler bought two tickets to a basketball game on the website Game Finder. Each ticket cost $65, and the website charged a convenience fee that was a small percent of the ticket cost. 

If Tyler’s total bill came to $132.60, what percent was the convenience fee? 

Guiding Questions

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Student Response

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Problem Set

15-20 minutes

Give your students more opportunities to practice the skills in this lesson with a downloadable problem set aligned to the daily objective.

Target Task

5-10 minutes

Lynn takes out a special loan for college students in the amount of $7,540. She is charged an annual simple interest rate of 6.5%. She does not need to make any payments for $$2\frac{1}{2}$$ years. 

How much will Lynn owe on her loan after $$2\frac{1}{2}$$ years?

Student Response

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Additional Practice

The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

Next

Solve percent applications involving measurement and percent error.

Lesson 11
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Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Percent, Part, and Whole

Topic B: Percent Increase and Decrease

Topic C: Percent Applications

Topic D: Scale Drawings

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