Lesson 19

The purpose of this lesson is for students to represent a two-digit number in more than one way, using tens and ones.

In a previous unit, students decomposed numbers to 20 in different ways. In previous lessons, students learned about the meaning of the digits in a two-digit number. They interpreted, used, and connected different base-ten representations for two-digit numbers including connecting cubes in towers of 10 and singles, base-ten diagrams, addition expressions, and written numbers.

In this lesson, students represent two-digit numbers in more than one way based on place value. Students learn that there are different ways to represent a two-digit number with tens and ones which will be important in a later unit when they compose a ten to add within 100.

• Each group of 3-4 needs a bag of connecting cubes in 5 towers of 10 and 4 or 5 handfuls of singles.

• Gather materials from previous centers:
  • Greatest of Them All, Stage 1
  • Get Your Numbers in Order, Stage 1
  • Grab and Count, Stage 2

In the next unit, students add within 100, including adding numbers that require composing a new ten when adding by place. How will the work of this section prepare students for the upcoming work with addition?