This Problem Set is a part of the Lesson 6, Unit 4, Grade 2. In this lesson, students apply their understanding of place-value strategies to the addition algorithm. They work concretely with place-value disks on a place-value chart to represent the composition of 10 ones as 1 ten with two-digit addends. The use of manipulatives reminds students that they must add like-units, for example, 26 + 35 is 2 tens + 3 tens and 6 ones + 5 ones).