Lesson 6

The purpose of this lesson is for students to add one-digit and two-digit numbers, with composing a ten, using place value understanding and the properties of operations. Students also make sense of equations that represent addition methods.

In this lesson, students add one-digit and two-digit numbers by composing a ten using place value reasoning and properties of operations. The associative and commutative property are highlighted in this lesson.

The first activity uses 10-frame diagrams to encourage students to determine how many ones can be added to a two-digit number to get to the next multiple of 10. Much like they did when looking to make a ten when adding within 20, students consider decomposing a one-digit number in such a way that they can combine one part with the two-digit number to make a multiple of 10 (\(68 + 6 = 68 + 2 + 4 = 74\)).

In the second activity, students compare different representations of this method, including those that use connecting cubes and base-ten drawings. These representations help students use their understanding of place value to see that when adding ones to ones, they can sometimes make a new unit of ten. This is a conceptual jump for students from understanding that they can count to a “10” (or the next ten) to understanding that they can create a new unit of ten from 10 ones (MP7).

Activity 2: Elena and Andre Add

How did the work of Activity 1 lay the foundation for students to be successful in the next activity? What do students need to be fluent with in order to use the method presented in Activity 2?