The purpose of this activity is for students to determine the unknown addend in equations with sums that are multiples of 10. The first two problems are represented using both ten-frames and equations to encourage students to visualize the unknown addend. Students may initially find the unknown addend using fingers or math tools, then see that they can use known facts to combine the ones to make ten.

During the Activity Synthesis, the teacher records equations to show how the student decomposed the two-digit addend and used a known fact to make ten. For example, to solve , the teacher records:

This notation and the discussion that follows can help students transition from counting on to the next ten to using the facts they know within 10 to help them add within 100. This also prepares them for the next activity where they describe making a ten using place value understanding.

• Display 
• Invite students to share their thinking.
• After the first student shares, record
• “How does this equation match how they thought about the problem?” (42 can be broken apart into 40 and 2. To get to the next ten, which is 50, they can think about what can be added to 2 to get 10. and .)
• If needed, consider asking:
  • “Where is 42 in this equation?”
  • “Where is 10 in this equation?”

The purpose of this activity is for students to add one-digit and two-digit numbers with composing a ten and deepen their understanding of place value. In this activity, students make sense of two different addition methods where an addend is decomposed to make a ten. Students then determine the next step needed to find the value of the original sum. Invite students to use different representations to make sense of these methods including connecting cubes and base-ten drawings. Completing the start of a calculation as students do here requires critically analyzing, understanding, and expressing different strategies (MP3).

Students then have an opportunity to add using one of these methods and the representations that make sense to them. Monitor for students who show composing a new unit of ten using connecting cubes or base-ten diagrams. Students use appropriate tools strategically as they choose which tools help them add (MP5). As selected students share their thinking during the Activity Synthesis, record their thinking as drawings and equations so that students can connect the method to the concept of making a new unit of ten from 10 ones.

For example:

• “How are Elena and Andre’s methods alike? How are they different?” (They are alike because they both made a ten. They are different because Elena showed making a ten with the 4 ones from 34 and 6 ones from the 9. Andre made a ten with the 9 ones and one of the ones from 34.)
• Invite previously identified students to share their representations for . Consider beginning with students who used connecting cubes to show composing a ten before students who use only equations.
• If needed, record student thinking with base-ten drawings and equations (see the Activity Narrative for an example).
• “How does this equation match the representation?” (They drew 6 tens and 8 ones for 68 and 6 ones for the 6. They showed they combined the 8 ones with 2 ones to make a ten. That matches the part of the equation that shows . They showed they counted 60, 70, and 4 more to get to 74. That matches the equation  .)

The purpose of this activity is for students to learn a new center called Target Numbers. Students add a one-digit number to a two-digit number with composing a ten in order to get as close to 95 as possible. Students take turns picking a number card, adding it to their starting number for the round, and writing an equation. Students start their first equation with 55 and then the sum becomes the first addend in the next round. The player who gets closest to 95 in 6 rounds, without going over, is the winner. Students may use any method they want to find the value of each sum. Students should be encouraged to think about how they can decompose the one-digit number in order to compose a new ten. During the Activity Synthesis, the teacher records equations that match student thinking and encourages students to make connections between the equation and how the student found the sum.

• Invite previously identified students to share.
• Record student thinking using equations.