# Algebraic Expressions Lesson 4 Episode 2 (Teachers)

### Making Sense

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Stop the video above first if it is playing.

The students continue exploring the scooter applet and see if their conjecture holds for negative and decimal values.

### Episode Supports

Students’ Conceptual Challenges

In the previous episode, ET and Haleemah make a hypothesis about Hector’s scooter ride that involves subtracting or adding the start position to the product of the time and velocity of the scooter ride [Episode 1, 6:30]. In this episode, they test this hypothesis and restate it, noting that “the trip time multiplied by the velocity can either subtract or add by the start location equals the distance traveled” [3:09]. However, both the scooter applet and their calculations result in Hector’s end location, not the distance he traveled.

Focus Questions

For use in a classroom, pause the video and ask these questions:

1. [Pause the video at 2:00] Haleemah and ET are about to see what happens when Hector starts at –15 meters from home (i.e., 15 meters to the west of home) and rides his scooter for 2 seconds with a velocity of –6.5 meters per second. Ask your students to make a prediction: Will Hector end up east or west of his home? How far east or west? How do they know?
2. [Pause the video at 2:37] Ask your students if multiplying the trip time by the velocity will help ET and Haleemah determine Hector’s end location. Ask them to explain how it might help and what else they may need to do to determine the end location.

Supporting Dialogue

Restate ET and Haleemah’s hypothesis, namely that multiplying the trip time by the velocity and then either adding or subtracting the start location will give the distance traveled. Ask them if they agree or disagree. If they agree, ask them for evidence. If they disagree, ask how they would change the hypothesis to make it true.