Kate and Christopher anticipate how many groups of the blue car’s journey (10 miles in 4 minutes) will fit in the red car’s journey, when the red car travels 65 miles in some unknown number of minutes. Then they use this information to figure out how long the red car should take so that it goes the same speed as the blue car.
For use in a classroom, pause the video and ask these questions:
1. [Pause video at 2:22] Kate and Christopher wrote a mathematical sentence. What are the units for each number in the sentence? What quantity does each number enumerate?
2. [Pause video at 4:18] First, Christopher numbered each group. Then he put a zero to the right of each group number. What does the zero represent? What happens when he adds a 0 after the .5?
Support students’ ability to build on an argument while using precise language by asking students to:
1. Pause the video at 6:11. What are the units for each number in the math sentences?
2. Work with your neighbor to write an explanation of how the number sentences represent that both cars are going the same speed. Concentrate on using precise language in your argument.