In this lesson, students continue to apply knowledge of place value to add numbers up to 1,000. They continue to add multiples of 100 with the added complexity of some tens. Students also use arrow notation to record their mental math. Problems are chosen so that, at first, the tens digit is close to a multiple of 100 (e.g., 190, 290, 380) to make it easier to form the next hundred by decomposing addends. This prompts students to analyze and use relationships between numbers to develop a variety of simplifying strategies.