In this video lesson, students subtract signed numbers on a number line by relating it to an addition equation with a missing addend. Students see that a subtraction equation like -8 – 3 = ? can be thought of as the related addition equation 3 + ? = 8. After repeatedly calculating differences this way (MP8), students recognize that the answer to each subtraction problem is the same number they would get by adding the opposite of the number. For example, -8 – 3 = ? can also be thought of as -8 + -3 = ?

Grade 7, Episode 10: Unit 5, Lesson 5 | Illustrative Math