Unit 5
Adding within 100
Unit Goals
- Students use place value understanding and properties of operations to add within 100.
Unit Narrative
In this unit, students add within 100, using place value and properties of operations in their reasoning.
In a previous unit, students composed, decomposed, and compared numbers within 100. They reasoned about units of tens and ones and represented numbers with connecting cubes, base-ten drawings, expressions, and equations in different ways (for example,
Students begin by adding a two-digit number with another two-digit number or with a one-digit number where it is not necessary to compose a new ten. Then they observe cases in which adding some ones together requires composing a new ten.
Two broad methods for finding sums are explored: adding on by place (adding on tens, then ones), and adding units by place (combining tens with tens and ones with ones).
They also compare methods from earlier work, such as counting on and making use of known sums, including sums of 10.
Add on tens, then add on ones:
Students make sense of methods for adding (especially as it relates to composing a ten when adding ones and ones). They work with a variety of representations—connecting cubes in towers of 10 and singles, base-ten drawings, expressions, and equations. They also use different representations to share their thinking with others.
Expressions and equations are presented horizontally to encourage students to make sense of the numbers and ways of adding rather than apply an algorithm. Eventually, students write equations to represent their thinking. For example, to find the sum of
or
Students are not expected to write or use equations in any specific way. Even in activities that focus on interpreting and writing equations, students should have continued access to drawings and other tools. Provide access to connecting cubes in towers of 10 and singles throughout the unit.