Lesson 15

Changing the Score

These materials, when encountered before Algebra 1, Unit 5, Lesson 15 support success in that lesson.

Lesson Narrative

Previously, students wrote expressions for percent increase or decrease using multiplication only. In this lesson, students explore applying percent increase or decrease repeatedly. Students see examples showing that applying a percentage more than once is not the same as adding the percentages and applying to the original once. In one activity students play a game, and calculate cumulative increases or decreases to running game scores. Then students look at the common error and explore the difference when applied incorrectly. This lesson helps prepare students for the associated Algebra I lesson involving compound interest and writing an expression in the form \((1+r)^n\) to represent a percent increase applied \(n\) times. When students explain why the common mistake that we are trying to avoid is a mistake, they are critiquing the reasoning of others (MP3).

Learning Goals

Teacher Facing

  • Recognize that increasing or decreasing by a percentage repeatedly applies to the new amount, not the original amount.

Student Facing

  • Let’s keep increasing or decreasing an amount by a percentage.

Required Preparation

You either need 1 number cube for each student, or each student needs access to a random number generator that can generate an integer between 1 and 6 inclusive.

CCSS Standards


Building Towards

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