Lesson 16

The purpose of this Number Talk is to elicit strategies and understandings students have for adding on to 10. These understandings help students develop fluency and will be helpful later in this lesson when students write equivalent expressions. 

• Display one expression.
• “Give me a signal when you have an answer and can explain how you got it.”
• 1 minute: quiet think time

• Record answers and strategy.
• Keep expressions and work displayed.
• Repeat with each expression.

• “Why did some of the expressions have the same value?” 

The purpose of this activity is for students to match expressions with three addends to the \(10 + n\) expression with the same value. This activity sets the groundwork for the next activity in which students make sense of addition equations with expressions on both sides of the equal sign. Students should have access to double 10-frames and two-color counters or connecting cubes.

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-color counters.

• Read the task statement.
• 8 minutes: partner work time

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?”

• “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.)

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.

• Groups of 2
• Give students access to double 10-frames and connecting cubes or two-color counters.

• 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 \(10 + 8 = 8 + 10\).

• 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 \(8 + 10\).)

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.

• 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.”

• 5 minutes: independent work time
• 3 minutes: partner discussion

• 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.