Reflection: Intervention and Extension Finding a Percent of Change - Section 1: Introduction


The bar model provides a nice pictorial model of finding percents of change for the majority of students.  However, I have several students who still benefit with more concrete models.  I worked with a few of these students during an intervention block later in the day using square color tiles.  Of course, you could use any similar manipulative.  I focused on given them problems that showed percents of change in multiples of 10% and 25%.  The formal starts with 20 tiles and the latter with 4.  

An example problem follows.  

Last week you worked 16 hours.  This week you only worked 12 hours.  What is the percent of change?

You might ask students to consider whether they want to model this using 10 tiles or 4 tiles.  This would provide an assessment of whether students understand why one model is more suitable than the others.  You may decide just to give the model.

We modeled this problem using 4 tiles.  Discuss the value of each tile (4 hours).  Discuss the percent represented by each tile (25%).  Ask how many tiles do we remove to end up with 12 hours?  What percent does this represent?  I wrote the formula with 16-12 / 20 or a 5% decrease to show the relationship between the actions with the tiles and the formula.   

  More Concrete Before Pictorial
  Intervention and Extension: More Concrete Before Pictorial
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Finding a Percent of Change

Unit 5: Percent and Proportional Relationships
Lesson 8 of 15

Objective: SWBAT find a percent of change using a formula

Big Idea: The amount of change over the original amount makes a fraction which can be changed to a percent.

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percentage change calculator
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