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 number 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, and then combining the sums (\(30 + 20 = 50\), \(2 + 5 = 7\), and \(50 + 7 = 57\)). They also consider adding on tens and then 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 ten must be composed. Students add a one-digit number and a two-digit number, such as \(68 + 6\). Students may compose a ten as they count on (\(68 + 2 + 4 = 74\)), as shown in the first image, or they may combine the ones and then add the tens (\(8 + 6 = 14\), \(14 + 60 = 74\)), as shown 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 in which order they combine the parts of each addend, the sum remains the same.

Explain how Jada, Kiran, and Tyler each find the value of \(37 + 25\).

Try it at home!

Near the end of the unit, ask your first grader to solve the problem:

 \(19 + 39\)

Questions that may be helpful as they work:

• Do you need to make a ten?
• How did you make a ten?
• Can you solve the problem in a different way?

Solution:
58

Sample response:

• Yes, I need to make a ten because when I add together the ones in each number, there are more than 10.
• I took 1 from 19 to make 40. Then I added: \(18+40=58\).
• I can add the tens first and then the ones, and then add together the two sums: \(10+30=40\), \(9+9=18\), \(40+18=58\).