Josh and Arobindo continue to investigate the growth of mold on a pizza. They use a number line to estimate how long it will take for the mold to increase by a factor of 10.
Episode Supports
Students’ Conceptual Challenges
One challenge that seems to be present for Josh is understanding that the amount of time it takes to increase from 1 gram to 10 grams is the same amount of time it takes to increase from 3 grams to 30 grams. He mentions that they have the same growth factor of 3, but it is unclear what he means by “they.” Additionally, for the periods of time they are examining, the growth factor is actually 10, and as the two students learned in the Project MathTalk unit on exponentials, equal time periods have equal growth factors, and vice versa.
Focus Questions
For use in a classroom, pause the video and ask this question:
[Pause the video at 0:50] Do you agree with Arobindo that it will take a little over 2 hours for the number of grams of mold to increase by a factor of 10? Why or why not?
Supporting Dialogue
Consider pausing the video before the recap [2:22]. Ask your students to discuss why it would take the same amount of time for the number of grams of mold to increase from 1 to 10 as it would from 3 to 30.
