Percent of change falls within the 7th grade standard domain of Ratios  & Proportional Reasoning. Knowing that students often struggle with this topic, I wanted to create a 3-act to aid in their understanding. I initially wanted to show the percent of decrease when making beef jerky. Due to aesthetics and cost, I dropped the beef jerky  idea and moved forward using the more cost effective mango.

Act 1: Dried Mango – Act 1

Act 2:

Before

Length of mango piece

Width of mango piece

Height of mango piece                            

After

Length of mango piece

Width of mango piece

Height of mango piece

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Act 3: The Reveal

Once finished with the first 2 acts, I sat looking at my computer wondering about how to organize The Reveal.  Desmos to the rescue.  I created a Desmos double number line to track the percent of decrease.

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Multiple Representations

In anticipation of

• student responses
• exposing students to various strategies
• and preparing to lead a whole class discussion by sequencing and  connecting differing strategies

my colleague, Mari, created the following summary.

Click here to see my other 3-act lessons.