In this video lesson, students add signed numbers as they build towards fluency. They see that adding a number and its opposite gives a sum of 0. They contrast adding numbers with the same sign with adding numbers with different signs. Using the structure of opposites on the number line, they see that when adding two numbers with different signs, the sign of the sum will match the sign of the addend with the greater magnitude (MP7). Students are also introduced to using negative numbers in the context of money to represent debts or debits.

Using a mathematical structure (the signed numbers) to represent a context (a checking account balance) is an example of modeling with mathematics (MP4).

Grade 7, Episode 9: Unit 5, Lessons 3 & 4 | Illustrative Math