This Problem Set is a part of the Lesson 8, Unit 6, Grade 1. In this lesson, students use Rekenreks and place-value charts to represent 100 as 10 tens and then represent 101 as 10 tens and 1 one, 102 as 10 tens and 2 ones, etc. This work with the unit form of numbers to 120 supports students' understanding of the written numerals 101 through 109, which are the most challenging to write.