This Number Talk encourages students to think about how to use the addition and subtraction facts they know and their understanding of place value to mentally find values of expressions. The strategies elicited here will be helpful as students use the facts they know to develop fluency with addition and subtraction within 100.

Students may notice that calculating is repeated in each expression, and they use this pattern to mentally find the values (MP8). Students must also attend to precision when they describe how they use known facts or other methods (MP6), especially when they describe subtracting by place. Encourage students to tell more about their strategy if they use unclear language and to reflect on how their description could be interpreted differently without more precise language. For example, if students say they knew because they know , ask students to explain how that fact helped them subtract the two-digit numbers.

• “How is each expression like ? How are the expressions different?” (Each expression has the digits 6 and 3. In each expression, we can use what we know about . In some expressions, we find 6 ones 3 ones. In some expressions, we find 6 tens  3 tens.)