In previous lessons, students learned how to use an algorithm that records a single digit for the sum in each place-value position, but records 10 or 100 for a newly composed ten or hundred. The purpose of this lesson is for students to continue to work with algorithms, but see that newly composed tens or hundreds can be recorded as a single digit at the top of the tens column or hundreds column. Students also take time to consider when it makes sense to use an algorithm and when it makes sense to use another strategy, such as those learned in grade 2. Students will consider how thinking about the numbers in the problem can help them use their knowledge of addition flexibly to add within 1,000.

This lesson has a Student Section Summary.

What surprised you most about student thinking as they learned how to use algorithms for adding multi-digit numbers?