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.
Communicating Mathematically 