This Problem Set is a part of the Lesson 9, Unit 1, Grade 5. In this lesson, students begin to model addition of decimals. They first model addition of decimals using place value chips and charts. For example, students model the addition of 2 tenths + 6 tenths, 2 ones 3 thousandths + 6 ones 1 thousandth, and 2 tenths 5 thousandths + 6 hundredths.