# Algebraic Expressions Lesson 2 Episode 2 (Teachers)

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The students apply their method for finding the number of tiles in the border to swimming pools of different sizes.

### Episode Supports

Students’ Conceptual Challenges

As in the previous lesson, Haleemah and ET were able to apply their method to pools of different sizes. This time, ET confuses multiplication and addition when he says “So now we need to do seven times seven times seven times seven, or seven times four” [0:58]. Recognizing appropriate operations for a given context can be challenging, but this skill contributes to a student’s ability to accurately and efficiently reason quantitatively.

Focus Questions

For use in a classroom, pause the video and ask this question:

[Pause the video at 0:45 and/or 3:16] Ask students to use Haleemah and ET’s new method to find the number of tiles in the border of a pool with 7 and/or 15 tiles on one side.

Supporting Dialogue

1. Display the two equations from the video: (7 • 4) – 4 = 24 and (15 • 4) – 4 = 56. Ask students to identify what seems to change and what seems to stay the same across the equations. This move helps students begin to generalize, which is something Haleemah and ET do in the next video.
2. Encourage students to reason abstractly and quantitatively by focusing on the arithmetic operations in ET and Haleemah’s equation. Ask them to explain to a partner why there is a “times 4” in the equation and what the “minus 4” means in the pool context. You can replay the video from 1:00 to 1:15 and ask students to justify whether or not seven times seven times seven times seven is the same as seven times four.