Lesson Objective: Understand that the relationship between distance traveled and time elapsed may be proportional, and we can report that relationship with one number representing a speed.

Students will work toward understanding that we can use unit rates with unlike units, such as distance and time. In grade 6 students began this work, but this is the first time they will use fractions in distances and rates of speed. The use of a double number line supports this relationship as students deepen their understanding of the unlike units changing together in a constant way.

Students engage in Mathematical Practices 4 and 6 in this lesson. They model a complex scenario using a double number line (MP.4), which helps them make sense of a situation involving seconds as fractions of minutes and laps as fractions of miles, with both decimal and fraction notation being used. This complexity also requires that students use MP.6, attending constantly to precision as they convert units and change notations.

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