This Problem Set is a part of the Lesson 6, Unit 2, Grade 1. In this lesson, students continue to focus on adding 9 and another single-digit number. In particular, they recognize that either addend can be decomposed in order to make 10 and another number. For example, students add 5 + 9 in two ways: by decomposing 5 to make 4 + 1 + 9 = 4 + 10 = 14, and by decomposing 9 to make 5 + 5 + 4 = 10 + 4 = 14.