In this lesson, students extend base ten understanding to numbers within 200. Students use chip models and arrow notation. For example, students solve 50 + 80 by thinking 5 tens + 8 tens = 13 tens = 130. They work to compose 10 tens as 1 hundred. Students use place-value language to explain where they make a new hundred. They also relate 100 more to + 100 and mentally add 100 to given numbers.