Unit 2, Lesson 9
Add and Subtract within 100
Grade 2
Warm-up
Which Three Go Together: Tens and Ones
Instructional Routines
Which Three Go Together?Materials
NoneActivity Narrative
This Warm-up prompts students to carefully analyze and compare features of base-ten diagrams. In making comparisons, students look for and make use of structure as they describe representations of tens and ones, and as they describe the values shown with the base-ten diagrams (MP7). This Warm-up gives the teacher an opportunity to hear how students use terminology and talk about characteristics of base-ten diagrams, including equivalent representations (MP6). This will be important as students compose and decompose two-digit numbers as they add and subtract within 100.
Launch
- Groups of 2
- Display the image.
- “Pick 3 that go together. Be ready to share why they go together.”
- 1 minute: quiet think time
Activity
- “Discuss your thinking with your partner.”
- 2–3 minutes: partner discussion
- Share and record responses.
Which 3 go together?
Activity Synthesis
- “Why do all 4 go together?” (They are all base-ten diagrams. They all show 40 in different ways. B and D use tens. A uses 3 tens and 10 ones. C uses ones but they are organized in groups of ten.)
Student Section Summary
We added two-digit numbers. We composed 1 ten by putting 10 ones together. We also subtracted two-digit numbers. We decomposed 1 ten by breaking it apart into 10 ones. We used base-ten blocks and base-ten diagrams to show our thinking.
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