7-5.6 Subtracting Rational Numbers

I have included my first attempt at putting an OpenMiddle problem into AB (Slide 8). Hopefully a better template for doing this will evolve! Student Facing Goals I can find the difference between two rational numbers. I understand how to subtract positive and negative numbers in general. Lesson Narrative In this lesson, students see that the `difference` between two numbers can be positive or negative, but the distance between two numbers is always positive. Using the geometry of the number line (MP7), they see that if you switch the order in which you subtract two numbers, the difference becomes its opposite. For example, to find the difference in temperature between +70 and +32 we calculate , so the difference is 38. The distance between these two is also 38. On the other hand, to find the difference in temperature between +32 and we calculate , so the difference is . The distance is still 38. In general, if , then . By observing the outcome of several examples, students may conjecture that this is always true (MP8).

By Jeff Holcomb