The purpose of this activity is for students to learn a subtraction algorithm that records the difference in each place-value position as a single digit. The algorithm also records a decomposed hundred as a single digit in the hundreds place and as two digits in the tens place. Students carefully analyze and discuss two different ways to subtract, highlighting similarities and differences, and explaining how and why they work (MP6).

• Invite students to share their work for completing each algorithm.
• “What did you do differently as you completed each problem?” (With Andre’s work, I subtracted all the place values, and then I added up all the parts of the difference. With Clare’s work, once I subtracted the digits in each place value, the answer was complete.)

The purpose of this activity is for students to practice using the algorithm they learned in the previous activity, in which the difference in each place-value position is recorded with one digit, and the decomposition of a place-value unit is recorded with one or two digits.

• Display students' work on the first expression.
• “Where do we see the 91 after the 9 and the 1 have been crossed out?” (The 8 and the 11 represent 80 and 11, which is 91.)