In this activity, students examine two tables of information related to the Aral Sea. They choose what pairs of values to compare, and they calculate the percent increase or decrease between the values. They write sentences describing what each percentage represents about the situation. As students choose what aspects of the data to focus on for their calculations,  they are making sense of the problem (MP1). As students clearly state what each percentage represents, about the situation, they are attending to precision (MP6).

The purpose of this discussion is for students to attend to precision in the language they use to describe how their percentages represent the situation with the Aral Sea. If time permits, ask students to prepare a display that shows their percentages and sentences. Encourage students to include details that will help others interpret their thinking. 

Invite several students to share one of their sentences. Ask the class to respond to the sentence. This could include restating in their own words how the percentage represents the situation with the Aral Sea or giving feedback that would help clarify or strengthen the sentence. Consider asking:

• “What kinds of additional details or language helped you understand the percentage?”
• “Were there any additional details or language that you have questions about?”
• “Did anyone calculate the same percentage but would explain it differently?”
• “What did the sentences have in common? How were they different?”

Invite students to think about how the percentages they calculated tell a story with the data. Consider asking:

• “How did you decide which percentages to compare?”
• “How did the way you reported the values impact the conclusions that could be made?”
• “How might the data have been described in a news report?”

In this activity students apply reasoning about percent increase and decrease to information about the Great Barrier Reef. They calculate the percentage by which the coral coverage has decreased. They also calculate what the new area would be after a potential percent increase.

In the Are You Ready for More? task students explore a repeated percent increase. Although students have not learned about compounded rates, they can continue multiplying the area by 1.0089 until they reach the desired value, tracking the number of times they multiply. Students attempting this process may benefit from being shown how most calculators will use the result of the previous calculation and repeat the same operation when the “=” button is pressed repeatedly.

Invite students to share their sentences from the first question. Ask the class to give feedback on whether the sentence clearly describes what the percentage represents.