After having time to work on the task, Casey, one of the students, places his work on the board.  In this clip, Shannon directs a classroom discussion to review Casey’s work. She focuses on particular intervals and landmark points on the graph.

Now that the students have developed a possible graph representing the sum of the two functions, Ms. Coombs turns the attention to the meanings that the graph itself conveys.  She begins by asking when the combined population of the cities is decreasing.  In this clip we see how one student focuses on the shape of the graph to answer the question. 

In this clip we see Ms. Coombs continue to work the task dealing with how populations changed over time.  Here, Ms. Coombs extends the task and asks the students if they could estimate the overall change in population.

Shannon continues to discuss how to estimate the overall change in population. She directs students away from thinking of singular values to an overall accumulation across time.