Lesson 6
Use a Ten to Add Within 1,000
Warmup: Number Talk: Numbers that Make 10 (10 minutes)
Narrative
Launch
 Display one expression.
 “Give me a signal when you have an answer and can explain how you got it.”
 1 minute: quiet think time
Activity
 Record students’ thinking on an open number line and with equations.
 Keep expressions and work displayed.
 Repeat with each expression.
Student Facing
Find the value of each expression mentally.
 \(28 + 2\)
 \(28 + 12\)
 \(67 + 3\)
 \(67 + 23\)
Student Response
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Activity Synthesis
 “What’s the same about all of the expressions?” (I made a ten to find the value for each of them.)
 “Why are \(28 + 2\) and \(67 + 3\) helpful in finding the value of the other expressions?” (We made ten and then added 1 more ten.)
 “In the next activity, we are going to keep thinking about how knowing sums of 10 can help us.”
Activity 1: Add Twodigit and Threedigit Numbers (15 minutes)
Narrative
Required Materials
Materials to Gather
Launch
 Groups of 3
 Give students access to baseten blocks.
Activity
 “In your group, each of you will find the value of one set of expressions.”
 Make sure students know which set they will work with.
 “As you work, think about patterns you notice.”
 “If it helps, you may use baseten blocks.”
 6 minutes: independent work time
 “Compare with your group members and discuss any patterns you noticed.”
 4 minutes: partner discussion
Student Facing

Find the value of each sum.
Set 1
Set 2
Set 3
\(245 + 15\)
\(134 + 26\)
\(351 + 19\)
\(247 + 23\)
\(133 + 37\)
\(356 + 24\)
\(249 + 31\)
\(138 + 42\)
\(355 + 35\)
 What patterns did you notice?
Student Response
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Advancing Student Thinking
If students find a sum other than the sum of the two numbers, consider asking:
 “Can you explain how you found the sum?”
 “How could you use a number line or baseten blocks to show your thinking?”
Activity Synthesis
 “What patterns did you notice in each set?” (Each time we could make a ten with the ones. The number of hundreds didn't change. The sums went up by 10.)
 Share and record responses.
 “How does knowing \(6 + 4 = 10\) help you think about \(536 + 34\)?” (I can add \(530 + 30 = 560\). Then add 10 because I know \(6 + 4 = 10\).)
Activity 2: Card Sort: Perfect Ten (20 minutes)
Narrative
The purpose of this activity is for students use what they know about combinations of 10 to identify when a ten will be composed when adding a threedigit number and a twodigit number by place. Students are given a set of cards with threedigit numbers and twodigit numbers and work with their group to decide which numbers will make a ten with no extra ones when they are added together (a “perfect ten”). After finding all the matches, each group member chooses a pair and finds the value of the sum. In the synthesis, students discuss how they could tell a pair of numbers would make a ten by looking at the digits in the ones place. In upcoming lessons, students will use this understanding to anticipate when they may need to compose units when they add 2 threedigit numbers.
When they match numbers whose ones combine to make ten students look for and identify structure which can be helpful when finding sums (MP7).
Advances: Conversing, Reading
Supports accessibility for: Conceptual Processing
Required Materials
Required Preparation
 Create a set of cards from the blackline master for each group of 3.
Launch
 Groups of 3–4
 Give each group a set of cards and access to baseten blocks.
Activity
 “This set of cards includes threedigit numbers and twodigit numbers. Match each threedigit number to a twodigit number, so that when you add them together they will make a ten with no extra ones. When this happens, we are going to say the two numbers make a ‘perfect ten.’”
 “Work with your partner to justify your choices.”
 As needed, provide an example of two numbers that make a “perfect ten” from the previous activities.
 “After finding all the matches, each group member should choose a different pair of numbers and find their sum.”
 “If there is time, switch cards or pick another pair.”
 15 minutes: smallgroup work time
 Monitor for groups who focus on finding combinations of 10 in the ones place and explain their reasoning.
 Monitor for students to share how they add their pair of numbers to share in the lesson synthesis.
Student Facing
 Match each threedigit number to a twodigit number. When you add your numbers together they should make a ten with no extra ones.

Pick 1 pair of numbers and find the value of their sum. Show your thinking.
Student Response
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Activity Synthesis
 Invite groups to share the matches they made and how they know those cards go together.
 Attend to the language that students use to describe their matches, giving them opportunities to describe how they knew adding the numbers would result in composing a ten with no extra ones more precisely.
Lesson Synthesis
Lesson Synthesis
“Today you learned that when you add a twodigit number to a threedigit number, knowing sums of 10 can help you tell if you will need to compose a ten.”
Invite previously identified students to share how they found the value of their sums.
Share and record responses.
Cooldown: Find the Sum (5 minutes)
CoolDown
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