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A submarine is at an elevation of -100 feet (100 feet below sea level). These statements compare the elevations of four people to that of the submarine:
Clare’s elevation is greater than the elevation of the submarine. Clare is farther from sea level than the submarine.
Andre’s elevation is less than the elevation of the submarine. Andre is farther away from sea level than the submarine.
Han’s elevation is greater than the elevation of the submarine. Han is closer to sea level than is the submarine.
Lin’s elevation is the same distance away from sea level as the submarine’s.
Plot and label a possible location for each person’s elevation on the vertical number line.
The goal of this discussion is to emphasize the difference between elevation and distance from sea level. Begin by displaying the vertical number line from the Task Statement for all to see. Invite students to share possible elevations for each person and to share their reasoning about how the elevation satisfies each part of the given description. Record student responses on the display for all to see. If possible, record responses for Clare, Andre, Han, and Lin in different colors.
Then display this table for all to see.
| possible elevation |
compare to submarine |
distance from sea level |
|
|---|---|---|---|
| Clare | 150 feet | or 150 feet | |
| Andre | |||
| Han | |||
| Lin |
Explain how the first row for Clare has been filled in with one possible elevation of 150 feet. Fill in the rest of the table as a class, emphasizing the language of “greater than” and “less than” when completing the middle column and “absolute value” when completing the right column.
If time allows, ask students if it would be possible for a person to have an elevation less than the submarine’s and also be closer to sea level. (No, it would not be possible because any elevation less than that of the submarine would be below the submarine and must also be farther away from sea level.)