The purpose of this video lesson is to help students make sense of expressions, and reason about their position on the number line— whether the number is positive or negative, which of two numbers is larger, or whether two expressions represent the same number. They work through common misconceptions that can arise about expressions involving variables. They also reason about expressions in a and b, given the positions of a and b on a number line without a given scale. This helps develop the idea that the letters in an algebraic expression can be thought of as numbers, even if you don't know the value of a.

Students connect ideas about rational number arithmetic and the interpretation of negative quantities, such as negative time or negative rates of change. They solve problems with rational numbers in various contexts by making tables or numerical calculations. As students reason about the meaning of negative quantities, they engage in MP2.

Grade 7, Episode 15: Unit 5, Lessons 13 & 14 | Illustrative Math