The purpose of this activity is for students to reason about subtraction and write another subtraction expression to complete a partially-completed Number Talk routine. If there is time, students can facilitate their Number Talk with another group. Students are given three expressions and prompted to think of ways that they could be evaluated mentally. They then write a fourth expression, the value of which they could use similar reasoning, or the values of the first three expressions, to find.

• Select groups to share their last expression and their reasoning.
• As each group shares, ask others in the class if they used the same strategy to write their expression and if they arrived at a similar expression.

The purpose of this activity is for students to reason about addition and apply their reasoning to complete a partially-completed Number Talk routine. This time, students are given addition expressions and are asked to think about how the values of the sums could be found mentally. They then write two new addition expressions to complete the set.

• Select groups to share their two expressions and their reasoning.
• As each group shares, ask others in the class if they used the same strategy to write their expressions and if they arrived at similar expressions.

The purpose of this activity is for students to write a sequence of three subtraction expressions to complete a Number Talk with only one given expression. As in earlier activities, students consider strategies that they or others might use to mentally subtract numbers within 1,000. 

• Select groups to share their completed Number Talk, and ask the class how the groups might have chosen their expressions.

The purpose of this activity is for students to design a Number Talk from a blank slate. They can choose to write addition or subtraction expressions, but still consider possible ways that others might find the values of the expressions mentally. If there is time, allow students to facilitate their Number Talk with another group.

• Invite 1 or 2 groups to share their completed Number Talk or to facilitate it for the class.
• Alternatively, if time permits, allow groups to take turns facilitating their Number Talk with another group.