The purpose of this activity is for students to match expressions with three addends to the 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.

• “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 pattern to determine whether equations are true.

• 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 on the 10-frame. Yes, we see that is 10, and then there are 8 left. That is the same as .)

The purpose of this activity is for students to write a  expression that is equivalent to a given expression. Each expression given has three addends, two of which make a ten.

• Display each expression.
• “In order to make adding three numbers easier, we can rewrite each expression as a 10 plus another number expression.”
• Invite students to say the value of each  expression together.