The purpose of this discussion is to connect students’ work with the idea that a growth factor that is greater than 1 leads to a longer subsequent segment and a growth factor that is less than 1 (sometimes called a decay factor) leads to a shorter subsequent segment. Ask students to take a few minutes to look at the equations associated with segments that grow in length, and those associated with segments that shrink in length. Here are some questions for discussion:

• “What do all of the equations related to figures in which the second segment was longer have in common?” (When the numbers were divided, the solution was greater than 1.)
• “What do all of the equations related to figures in which the second segment was shorter have in common?” (When the numbers were divided, the solution was less than 1.)
• “How can you tell from an equation if a second segment will be longer or shorter?” (If the quotient is greater than 1, the second segment is longer, and if the quotient is less than 1, the second segment is shorter.)

The purpose of this discussion is to remind students that exponential relationships have a constant growth factor, and how to calculate that number.

Use Critique, Correct, Clarify to give students an opportunity to improve a sample written response to the question asking which relationship is not exponential by correcting errors, clarifying meaning, and adding details.

• Display this first draft:
  The graph of Medicine E does not show an exponential relationship. The points , , and are in a straight line, so it is a linear relationship.
  Ask, “What parts of this response are unclear, incorrect, or incomplete?” As students respond, annotate the display with 2–3 ideas to indicate the parts of the writing that could use improvement.
• Give students 2–4 minutes to work with a partner to revise the first draft.
• Select 1–2 students or groups to slowly read aloud their draft. Record for all to see as each draft is shared. Then invite the whole class to contribute additional language and edits to make the final draft even more clear and more convincing.

Invite students to share their responses and their reasoning process. If students write division and multiplication equations to make sense of the given information and extract the growth factor, write these equations next to the graph. To find the amount of medicine at 4 hours, highlight the approach of multiplying the amount at 3 hours by the decay factor that was found earlier in the previous question.