Lesson objective: Solve problems by using the fact that the rate of change of a linear function is constant.

This lesson provides an opportunity for students to apply their knowledge and understanding that the slopes between all pairs of points on a given line are equivalent to a real-life situation. Students are asked to calculate the rate at which various devices charge, and use this information to determine what the charge of each device will be at a certain time.

Key Concept students will use:

Skills students will use:

- calculating rate of change given two points
- finding additional points on a line given the slope and a point
- solving proportions (Grade 7, Unit 1)

Students engage in Mathematical Practice 1 (Make sense of problems and perservere in solving them) as they interpret the information provided about each device as a linear relationship, and figure out how to use this realization to find missing information. Students must also make sense of answers in terms of context, for example interpreting a device with a charge of "112 percent" as having been completely charged for some amount of time.

**Key vocabulary: **

- constant rate of change
- slope