The purpose of this Choral Count is for students to practice counting back by 10 and notice patterns in the count. These understandings help students develop fluency and will be helpful later in this lesson when students will need to decompose hundreds.
Launch
“Count back by 10, starting at 590.”
Record as students count.
Stop counting and recording at 390.
Activity
“What patterns do you see?”
1–2 minutes: quiet think time
Record responses.
None
Student Response
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Advancing Student Thinking
Activity Synthesis
“What comes after 390 if we keep counting back by 10? What comes after 300?”
Activity 1
Standards Alignment
Building On
Addressing
2.NBT.B.7
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.
Explain why addition and subtraction strategies work, using place value and the properties of operations.Explanations may be supported by drawings or objects.
The purpose of this activity is for students to use their knowledge of base-ten diagrams and place value to make sense of a written method. They describe how numbers, words, and equations can be used to represent the steps they have shown with other representations (MP2). Students will explore other ways to use equations, including the standard algorithm, in future grades. Although some grade 2 students may begin to use recording methods, such as the standard algorithm, it is important to encourage students to use the methods that make the most sense to them.
Launch
Groups of 2
Give students access to base-ten blocks.
Display Elena’s work.
“Take a minute to make sense of Elena’s subtraction.”
1–2 minutes: quiet think time
“Discuss Elena’s work with your partner.”
1–2 minutes: partner discussion
Share and record responses. Highlight responses that describe the numbers Elena is subtracting and how Elena shows decomposing units.
Activity
“Elena is finding the value of . Use base-ten blocks or a base-ten diagram to show Elena’s steps. Then finish Elena’s work. If you have time, work together to show a different way Elena could use numbers or equations to show her steps.”
7 minutes: partner work time
Monitor for student examples that record in a way similar to Elena, but use numbers to show the value of each place.
Elena’s thinking
Step 1
Step 2
Step 3
Use a base-ten diagram or blocks to show Elena’s steps.
Finish her work. Find the value of .
What is another way to use numbers or equations to show subtracting by place to find the value of ?
Student Response
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Advancing Student Thinking
If students rely on one way to show subtracting by place with numbers or equations, consider asking:
“How did Elena represent the value of each digit in 726 and 558?”
“What is another way you could represent the values of the digits and show subtracting by place?”
Activity Synthesis
Display a student representation of Elena’s steps with a base-ten diagram and 1 or 2 other representations that use numbers and equations.
“How are these representations the same? How are they different?” (All show decomposing a hundred and a ten to subtract. They all show subtracting hundreds from hundreds, tens from tens, and ones from ones. Each representation is different, including a base-ten diagram, numbers and words, and subtracting by place value.)
Activity 2
Standards Alignment
Building On
Addressing
2.NBT.B.7
Add and subtract within 1000, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method. Understand that in adding or subtracting three-digit numbers, one adds or subtracts hundreds and hundreds, tens and tens, ones and ones; and sometimes it is necessary to compose or decompose tens or hundreds.
Explain why addition and subtraction strategies work, using place value and the properties of operations.Explanations may be supported by drawings or objects.
The purpose of this activity is for students to practice subtracting within 1,000. Each student starts with a card that has a three-digit number on it. Students walk around the room and find a student with a different number. They find the difference between their numbers and write an equation to represent the difference. As time allows, students find a new partner. The numbers on the cards were chosen so any pair of numbers would require decomposing a hundred and a ten when subtracting by place. In addition to monitoring for ways students use written methods for subtracting by place, monitor for the ways students use what they know about the relationships between the numbers to choose a method. For example, if students are finding the value of , they may choose to add on 2 to 198 and count on by place, instead of decomposing a hundred and a ten.
MLR8 Discussion Supports. Invite students to take turns sharing how they subtracted and how they showed their thinking.Ask students to use precise mathematical language and their own words to restate what they heard. Display the sentence frame: “I heard you say . . . .” Original speakers can agree or clarify for their partner. Advances: Listening, Speaking
Engagement: Provide Access by Recruiting Interest. Invite students to generate a list of contexts that represent subtraction. Choose one of the contexts that connect to their personal backgrounds and interests to use when subtracting. Refer back to the context while students work. Supports accessibility for: Attention, Conceptual Processing
Launch
Groups of 2
Give each student a card.
Give students access to base-ten blocks.
Activity
“We are going to create our own subtraction expressions and find their values. You will walk around and find someone who has a card with a different number. Create an expression and find the difference between your numbers. Show your thinking.”
“Trade cards and find a new partner.”
12 minutes: partner work time
Monitor for students who represent subtracting by place with:
A base-ten diagram.
Numbers, words, or equations.
Find someone with a different number than you.
Find the difference between your numbers.
Show your thinking, using drawings, numbers, or words.
Trade cards. Find a new partner.
Partner 1:
Partner 2:
Partner 3:
Student Response
Activity Synthesis
Invite previously identified students to describe the steps they used to find the difference for one of their expressions.
Consider asking:
“What questions do you have for _____ about their steps or their representation?”
“How was your representation the same? How were your steps the same? How were they different?”
Lesson Synthesis
Display students’ work samples that were shared in the last Activity Synthesis.
“How are these representations the same? How are they different?” (They show different expressions. Some use base-ten diagrams and some use only numbers and equations. Each shows subtracting hundreds from hundreds, tens from tens, and ones from ones. Each shows decomposing units.)
“Which methods did you try today? Which methods do you like better?”
Standards Alignment
Building On
Addressing
2.NBT.A.2
Count within 1000; skip-count by 5s, 10s, and 100s.
