Proportions Lesson 2 Episode 4 (Teachers)

Repeating Your Reasoning

Download Math TaskLink to Geogebra applet Link to on-line calculator

Kate and Christopher find how long the red car should take to travel 2.5 miles so that it goes at the same speed as the blue car, which travels 10 miles in 4 minutes.

Episode Supports

Focus Questions

For use in a classroom, pause the video and ask these questions:

1. [Pause video at 1:34] Can someone revoice Christopher’s reasoning?

 2. [Pause video at 4:55] Can someone revoice Kate’s idea?

Supporting Dialogue

Support students’ ability to build on the mathematical claims of others by asking the students to:

1. Notice Christopher’s suggestion to find the number of minutes the red car needs to travel so that is travels 100 miles at the same speed as the blue car, which travels in 10 miles in 4 minutes. Can someone share their thinking about how to answer that question?

2. Notice that Christopher also suggested solving the same speed task for the case when the red car travels 80 miles. Talk with your neighbor about whether you think his suggestions of tasks where the red car goes 100 miles or 80 miles have something in common, or are they just random numbers of miles he is mentioning. Prepare to share your thoughts with the class.