Percent of Change

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SWBAT find the percent of change.

Big Idea

What’s the difference between a percent of increase and a percent of decrease?


5 minutes
  • POD

As students enter the room, they will have a seat, take out their Problem of the Day (POD) sheet and begin to work on the question on the SMARTboard. The POD allows students to use MP 3 continually based on the discussions we have about the problem each day.


Use the table below to answer the following questions.


Cost of Gallon of Gas






What was the cost of a gallon of gas in 1970?

What was the cost of a gallon of gas in 2010?

Did the cost of a gallon of gas increase or decrease from 1970 to 2010?

By how much did the cost increase?


30 minutes

To start the activity, I want to discuss the definition of the percent of change. I want students to understand that the change is change in the quantity and the original amount. We will have a group discussion asking students to talk about what it actually means. We will also talk about the percent increase versus the percent decrease. They should recognize that the change always relates to the original amount. As we talk through this, it may be helpful for students to make reference to the bar diagrams we created if they need to or write down important concepts.

After we discuss the vocabulary and concepts as a group, students will work in pairs to solve problems involving percent of change. I want students to talk about the relevant information to solve each problem and make decisions about how to set up each problem to work on a solution. All of their ratios should reference the original amount. Are they using ratios? If they are using ratios, are they using the original amount as part of the ratio? I will be listening to student discussions as they work and asking them questions about what they are doing to determine their level of understanding. As pairs finish their work, we will display the solutions on the SMARTboard and talk about each solution and the steps students took to find the solution. I am looking for the vocabulary students use and the conceptual understanding they present. Did any pair use bar diagrams in their solution or have we moved past the concrete model?

Vocabulary Focus

Percent of Change                       Original Amount

Percent of Increase                       Amount of Increase

Percent of Decrease                     Amount of Decrease


5 minutes


To end class, I want to get a gauge of where students are with determining change and reasoning the amounts of change. Based on the answers to this exit ticket, I will know if we need to do additional work on building the conceptual understanding. Do they really understand how to find the amounts?

How can two amounts of change be the same but the percents of change be different?