Show students the following visual math talk prompt and be prepared to pause the video where indicated:

Then ask students:

This car is parked on level 5.

The car is moved down 6 levels.

What level is the car on now?

Write an equation to represent this scenario.

In the first prompt from this string of related visual problems, students are asked to move the car down (or remove levels) from level 5 a total of 6 levels. The context was crafted so that it is clear that the car can move down below ground level and we’ll annotate those levels below ground using a negative sign.

When the car moves down 6 levels, we see there are only 5 levels until the ground floor (level 0) and one more level to go, bringing us to level -1.

Another approach is to leverage the zero principle by first decomposing -6 (or going down 6 levels) to -5 and -1 so level 5 and removing 5 levels cancel bringing the car to level 0. Then, we have a movement of -1 floors remaining to bring us to level -1.

Of course this action is very intuitive through the context of levels in a parking garage, however it is important to also annotate what we are doing using the symbolic representation for students to see the relationships involving integer operations of addition and subtraction. 

Facilitator note:

The integers in this context can be interpreted as a change or as quantities of floors. For example, if the car starts on the fifth floor above ground level (5), and moves down 6 floors, this can be expressed as the addition of 6 negative floors [5 + (−6)], or a subtraction of 6 floors (5 − 6). Both statements result in the same answer (−1). 

When a positive and a negative integer are added together, the result is negative if the absolute value of the positive integer is less than the absolute value of the negative integer.