Lesson 16
Add Three Numbers
Warm-up: Number Talk: Related Expressions (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 answers and strategy.
- Keep expressions and work displayed.
- Repeat with each expression.
Student Facing
Find the value of each expression mentally.
- \(7 + 10\)
- \(7 + 2 + 8\)
- \(10 + 9\)
- \(4 + 9 + 6\)
Student Response
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Activity Synthesis
- “Why did some of the expressions have the same value?”
Activity 1: Match Expressions (15 minutes)
Narrative
Advances: Conversing, Speaking
Supports accessibility for: Conceptual Processing, Visual-Spatial Processing
Required Materials
Materials to Gather
Launch
- Groups of 2
- Give students access to double 10-frames and connecting cubes or two-color counters.
Activity
- Read the task statement.
- 8 minutes: partner work time
Student Facing
Draw a line to match expressions with the same value.
expressions with 3 numbers
\(10 + \boxed{\phantom{3}}\) expression
- \(4 + 6 + 8\)
- \(3 + 6 + 7\)
- \(9 + 1 + 1\)
- \(8 + 4 + 2\)
- \(5 + 5 + 9\)
- \(7 + 3 + 3\)
- \(5 + 10 + 5\)
- \(4 + 7 + 6\)
- \(9 + 5 + 1\)
- \(1+ 10 + 1\)
\(10 + 1\)
\(10 + 2\)
\(10 + 3\)
\(10 + 4\)
\(10 + 5\)
\(10 + 6\)
\(10 + 7\)
\(10 + 8\)
\(10 + 9\)
\(10 + 10\)
If you have time: Write another expression with 3 numbers. 2 of the numbers should make 10.
Ask your partner to think of the matching \(10 + \boxed{\phantom{\frac{aaai}{aaai}}}\) expression.
Student Response
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Advancing Student Thinking
If students find the value of each three addend expression, rather than making a ten first, consider asking:
- “Can you explain how you know these expressions match?”
- “How can we use the numbers in this expression to make 10? After we make 10, what number is left to add? What expression does that match?”
Activity Synthesis
- “How did you know which expressions have the same value?” (I looked for ways to make 10 and the amount left to add.)
- “What patterns did you notice?” (They are all teen numbers. They are all 10 + facts.)
Activity 2: Is the Equation True? (10 minutes)
Narrative
The purpose of this activity is for students to determine whether equations with an expression on each side of the equal sign are true. Each equation has an expression with three addends on one side and a 10 +n expression on the other. Students do not need to find the value of each expression in order to determine if the equation is true, but some students may do so. In this activity, students have an opportunity to look for and make use of structure (MP7) because they apply the associative property and \(10 + n\) pattern to determine whether equations are true.
Required Materials
Materials to Gather
Launch
- Groups of 2
- Give students access to double 10-frames and connecting cubes or two-color counters.
Activity
- Read the task statement.
- 4 minutes: independent work time
- 3 minutes: partner discussion
- Monitor for a student who uses 10-frames and counters or drawings to show \(3 + 7 + 8\) as \(10 + 8\) and a student who uses reasoning that \(3 + 7 = 10\) and \(10 + 8 = 8 + 10\).
Student Facing
Determine whether each equation is true or false.
Be ready to explain your reasoning in a way that others will understand.
- \(7 + 3 + 4 = 10 + 4\)
- \(6 + 5 + 4 = 15 + 10\)
- \(9 + 10 = 9 + 10 + 1\)
- \(3 + 7 + 8 = 8 + 10\)
- \(5 + 10 + 5 = 10 + 10\)
If you have time:
- Make any false equations true.
- Write 1 equation that is true and 1 that is false.
Switch with your partner.
Student Response
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Activity Synthesis
- Invite previously identified students to share.
- “Does their reasoning prove whether the equation is true? Why or why not?” (Yes, we can see that it is \(10 + 8\) on the 10-frame. Yes, we see that \(3 + 7\) is 10 and then there are 8 left. That is the same as \(8 + 10\).)
Activity 3: Write Expressions (10 minutes)
Narrative
The purpose of this activity is for students to write a \(10 + n\) expression that is equal to a given expression. Each expression given has three addends, two of which make a ten.
Required Materials
Materials to Gather
Launch
- Groups of 2
- Give students access to double 10-frames and connecting cubes or two-color counters.
- “Now you will write a \(10 + n\) expression with the same value as each of the given expressions.”
Activity
- 5 minutes: independent work time
- 3 minutes: partner discussion
Student Facing
Write a \(10 + \boxed{\phantom{3}}\) expression that has the same value as each expression.
- \(5 + 7 + 5\)
- \(3 + 7 + 6\)
- \(1 + 9 + 9\)
- \(4 + 8 + 6\)
- \(8 + 10 + 2\)
If you have time, write as many expressions as you can with 3 numbers that are equal to \(10 + 5\).
Student Response
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Activity Synthesis
- Display each \(10 + n\) expression.
- “In order to make adding three numbers easier, we can rewrite each expression as a \(10 + \boxed{\phantom{3}}\) expression.”
- Invite students to say the value of each \(10 + n\) expression together.
Lesson Synthesis
Lesson Synthesis
Give students access to double 10-frames and connecting cubes or two-color counters.
Display \(2 + 6 + 8 = 7 + 3 + 6\).
“Today we worked with expression with three numbers and expressions with 10. Is this equation true or false? How do you know?” (True. \(2 + 8 = 10\), \(10 + 6 = 16\). \(7 + 3 = 10\). \(10 + 6 = 16\).)
If needed, “Did anyone determine whether it is true or false without adding all the numbers?” (Yes. Both sides have a 6, so I looked to see if the other numbers made 10. \(2 + 8 = 10\) and \(7 + 3 = 10\), so both sides of the equation are equal to \(10 + 6\).)
Cool-down: Add Them Up (5 minutes)
Cool-Down
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