Lesson 9

This warm-up prompts students to compare four representations of a quantity. It gives students a reason to use language precisely (MP6). It gives the teacher an opportunity to hear how students use terminology and talk about characteristics of the items in comparison to one another. During the synthesis, ask students to explain the meaning of any terminology they use, such as tens, ones, number, and digit.

• Groups of 2
• Display the image.
• “Pick one that doesn’t belong. Be ready to share why it doesn’t belong.”
• 1 minute: quiet think time

• “Discuss your thinking with your partner.”
• 2–3 minutes: partner discussion
• Share and record responses.

• “How are C and D the same? How are they different?" (In both of them you can see the three groups of 10 and five ones. They are different because in C the ones are first and in D the tens are first.)

The purpose of this activity is for students to represent a two-digit number in as many ways as they can. Students are given two number cards and use them to make a two-digit number. Students then create a collection with connecting cubes in towers of 10 and singles to represent their number. Then, students represent their number in as many different ways as they can on paper. Representations may include base-ten diagrams, _____ tens _____ones, and expressions that show the tens and ones.

The collections students make are used in the next activity.

• Groups of 2
• Give each group two number cards and connecting cubes in towers of 10 and singles.
• “Use your number cards to make a two-digit number and write the number in the blank.”
• 30 seconds: partner work time

• “Work with your partner to create a collection of cubes that shows the number you wrote. Then each partner will show your number in as many ways as they can in your book.”
• 8 minutes: partner work time

• “How did you use the digits in the two-digit number you created to figure how to make the collection of connecting cubes?” (I know the digit on the left shows how many tens, so we got that many towers of ten. The digit on the right shows how many ones, so we got that many single cubes.)
• “How did you use the digits to create other representations?” (I used the digits to see how many tens and ones to draw. I know the digit on the left means tens and the other digits is ones, so I wrote it like __ tens and __ ones.)
• “Now you will do a gallery walk, observe other collections, and show them in as many ways as you can.”

The purpose of this activity is for students to represent a collection of tens and ones in as many ways as they can. Students participate in a gallery walk in which they visit at least four collections, represent them in different ways, and then compare their representations with their partner. Students may represent in any ways they choose, which may include base-ten drawings with and without showing all the ones within each ten, _____ tens _____ ones, expressions that show the tens and ones, or another way that makes sense to them, including writing the two-digit number.

Students may choose which collections they would like to visit or the teacher may assign the collections. During the activity synthesis, students make connections between representations.

This activity uses MLR7 Compare and Connect. Advances: Representing, Conversing.

• Students’ collections from the previous activity are needed for the gallery walk.

• Groups of 2
• Make student collections from the previous activity accessible for the gallery walk.

• Read the task statement.
• 10 minutes: gallery walk

If students only use one type of representation, consider asking:

• “What’s another way you could show this collection?”
• “How could you use words to describe this collection? How could you use numbers and symbols?”

MLR7 Compare and Connect

• Find a new partner and share the representations you made. 
• Discuss how your representations are the same and how they are different.
• Invite 2–3 groups to share what they discussed.

The purpose of this activity is for students to choose from activities that offer practice adding and subtracting within 20, or estimating, counting and representing quantities. Students choose from any stage of previously introduced centers.

• Grab and Count
• Shake and Spill
• Check It Off

• Gather materials from previous centers:
  • Grab and Count, Stage 2
  • Shake and Spill, Stages 3–5
  • Check It Off, Stages 1–3

• Groups of 2
• “Now you are going to choose from centers we have already learned.”
• Display the center choices in the student book.
• “Think about what you would like to do.”
• 30 seconds: quiet think time

• Invite students to work at the center of their choice.
• 10 minutes: center work time

• “Kiran is playing Grab and Count. He organized his cubes into 3 groups of ten and 1 one. How many cubes does he have?”