Logarithms Lesson 1 Episode 4 (Teachers)

The students create an expression that represents the height of the beanstalk 5 days after an unknown start date, and create a number line to represent this expression.

Episode Supports

Students’ Conceptual Challenges

Arobindo says, “We are varying the starting day” and then calls it Day y [0:23]. Some students might not decide this so quickly and may wonder where the starting day should go and what it should be called. You can prompt them to consider how they have handled similar mathematical situations in the past: What do they do when they have an unknown quantity that they need to represent?

Focus Questions

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

[Pause the video at 2:52] Why does the beanstalk grow 3y for the first part of the number line and 35 for the second?

Supporting Dialogue

1. In previous episodes, Arobindo had a method for writing the height of the beanstalk for some number of days after Day 2. In this video, his method seems to be missing. Prompt your students to make a prediction for what expression Arobindo might write for the height of the beanstalk 5 days after some number of days.
2. Arobindo’s method in previous episodes was to write the height of the beanstalk on Day 2 multiplied by the growth factor over some number of days. For this episode, we might expect him to write 3× 35. Ask your students if this expression represents the height of the beanstalk 5 days after some number of days. Ask them to make connections between the expression and the beanstalk context or the number line to support their argument.