In the associated Algebra 1 lesson, students will need to be able to do some subtraction, multiplication, and distributive property with fractions in order to access the new learning about constructing an expression to represent exponential decay. For example, think about this question: “The price of a new car is $18,000, which depreciates by each year. What is its value after years?” In order to do this, we need to know that decreasing 18,000 by (or ) is the same as multiplying it by (or , which is ), and that we are multiplying each new value by each year. So, the value after years is .

The purpose of this support lesson is to remind students of what it means to subtract, multiply, and apply the distributive property when fractions are involved. First, students perform numerical calculations, and then encapsulate the process using a variable. This is an example of expressing regularity in repeated reasoning (MP8). Then, students explain why some given pairs of expressions are equal, and then apply that reasoning to match some new pairs of expressions. This is an opportunity to notice and make use of structure (MP7).