# Logarithms Lesson 5 Episode 4 (Teachers)

The students explore a different moldy food–a peanut butter sandwich. The mold on the sandwich increases by a factor of 4 each hour. The students write a logarithmic expression that describes when the sandwich will have 200 grams of mold.

### Episode Supports

Focus Questions

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

1. [Pause the video at 0:48] Before watching Josh and Arobindo, try this task for yourself: Write a logarithmic expression to represent the time at which Harry’s peanut butter sandwich has 200 grams of mold on it, if it starts with 1 gram of mold and the mold increases by a factor of 4 each hour.
2. [Pause the video at 2:34] Arobindo has written 4log4200 = 200. Is this equation true? Use what you know about exponentials and logarithms to justify your answer.

Supporting Dialogue

Ask your students to consider the logarithmic relationship log4200 ≈ 3.82 and tell a partner what it means in the context of the moldy peanut butter sandwich.