Adding Within 100
In this unit, students use place value understanding and properties of operations to add within 100.
Section A: Add Without Making a Ten
In this section, students add a one-digit and a two-digit number, or 2 two-digit numbers within 100 without composing a ten. For example, \(32 + 25\). Students consider adding tens and tens and ones and ones (\(30 + 20 = 50\), \(2 + 5 = 7\), and \(50 + 7 = 57\)) and adding on tens and ones (\(32 + 20 = 52\), \(52 + 5 = 57\)).
Section B: Add One-Digit and Two-Digit Numbers with Making a Ten
In this section, students are introduced to the idea that sometimes when adding numbers within 100, a new ten must be composed. Students add one-digit numbers and two-digit numbers like \(68 + 6\). Students may compose a new ten as they count on (\(68 + 2 + 4 = 74\)), seen in the first image, or they may combine the ones and then add the tens (\(8 + 6 = 14\), \(14 + 60 = 74\)), seen in the second image. Students represent their thinking with drawings, expressions, or equations.
Section C: Add within 100, Making a Ten
In this section, students apply what they learned to add any numbers within 100. Students see that no matter which order they use to combine parts of each of the addends, the sum remains the same.
Try it at home!
Near the end of the unit ask your student to do the following problem:
\(19 + 39\)
Questions that may be helpful as they work:
- Do you need to make a new ten?
- How did you make a new ten?
- Can you solve the problem in a different way?