In a previous unit, as well as a previous section in this unit, students related addition to subtraction and thought about how knowing their addition facts to 10 could help them find differences.

The work of this lesson builds on students understanding of the relationship between addition and subtraction. In the first activity, students analyze two different methods for solving the same subtraction problem. Then they try each method with new problems. In the second activity, students find the value of the difference in subtraction equations and find the value in unknown addend equations.

With which math ideas from today’s lesson did students grapple most? Did this surprise you or was this what you expected?