Learn on PengiReveal Math, AcceleratedUnit 3: Solve Problems Involving Percentages

Lesson 3-3: Solve Percent Change Problems

In this Grade 7 lesson from Reveal Math, Accelerated, students learn how to calculate percent change — both percent increase and percent decrease — using the percent equation (amount of change = percent change × original amount) and tape diagrams. The lesson applies these skills to real-world contexts such as Arctic sea ice loss, social media growth, and changes in wealth distribution. Students practice identifying the original amount and the amount of change to solve for an unknown percent change, rounding results to the nearest tenth of a percent.

Section 1

Identify Percent Increase or Decrease

Property

To determine the type of percent change:

  • If new amount >> original amount, then percent increase
  • If new amount << original amount, then percent decrease
  • If new amount == original amount, then no change (0%)

Examples

Section 2

Steps to Find Percent Change

Property

To find the percent change:

  • Step 1. Find the amount of change.
change=new amount−original amount\text{change} = \text{new amount} - \text{original amount}
  • Step 2. Find what percent the amount of change is of the original amount. The amount of change is what percent of the original amount?
Percent Change=Amount of ChangeOriginal Amount×100%\text{Percent Change} = \frac{\text{Amount of Change}}{\text{Original Amount}} \times 100\%

Examples

  • A shirt's price increased from 20 dollars to 25 dollars. Find the percent change. The change is 25−20=525 - 20 = 5 dollars. The percent change is 520=0.25\frac{5}{20} = 0.25, which is a 25% increase.
  • A car's value decreased from 15,000 dollars to 12,000 dollars. Find the percent change. The change is 12,000−15,000=−3,00012,000 - 15,000 = -3,000 dollars. The percent change is−300015000=−0.20\frac{-3000}{15000} = -0.20, a 20% decrease.

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Unit 3: Solve Problems Involving Percentages

  1. Lesson 1

    Lesson 3-1: Connect Percentages and Proportional Reasoning

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  2. Lesson 2

    Lesson 3-2: Understand the Percent Equation

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  3. Lesson 3Current

    Lesson 3-3: Solve Percent Change Problems

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  4. Lesson 4

    Lesson 3-4: Solve Markup and Markdown Problems

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  5. Lesson 5

    Lesson 3-5: Solve Simple Interest Problems

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  6. Lesson 6

    Lesson 3-6: Solve Percent Error Problems

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Lesson overview

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Section 1

Identify Percent Increase or Decrease

Property

To determine the type of percent change:

  • If new amount >> original amount, then percent increase
  • If new amount << original amount, then percent decrease
  • If new amount == original amount, then no change (0%)

Examples

Section 2

Steps to Find Percent Change

Property

To find the percent change:

  • Step 1. Find the amount of change.
change=new amount−original amount\text{change} = \text{new amount} - \text{original amount}
  • Step 2. Find what percent the amount of change is of the original amount. The amount of change is what percent of the original amount?
Percent Change=Amount of ChangeOriginal Amount×100%\text{Percent Change} = \frac{\text{Amount of Change}}{\text{Original Amount}} \times 100\%

Examples

  • A shirt's price increased from 20 dollars to 25 dollars. Find the percent change. The change is 25−20=525 - 20 = 5 dollars. The percent change is 520=0.25\frac{5}{20} = 0.25, which is a 25% increase.
  • A car's value decreased from 15,000 dollars to 12,000 dollars. Find the percent change. The change is 12,000−15,000=−3,00012,000 - 15,000 = -3,000 dollars. The percent change is−300015000=−0.20\frac{-3000}{15000} = -0.20, a 20% decrease.

Book overview

Jump across lessons in the current chapter without opening the full course modal.

Continue this chapter

Unit 3: Solve Problems Involving Percentages

  1. Lesson 1

    Lesson 3-1: Connect Percentages and Proportional Reasoning

    LearnPractice
  2. Lesson 2

    Lesson 3-2: Understand the Percent Equation

    LearnPractice
  3. Lesson 3Current

    Lesson 3-3: Solve Percent Change Problems

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  4. Lesson 4

    Lesson 3-4: Solve Markup and Markdown Problems

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  5. Lesson 5

    Lesson 3-5: Solve Simple Interest Problems

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  6. Lesson 6

    Lesson 3-6: Solve Percent Error Problems

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