Ask a student to show how to solve Question 1B, 1489 – 597, on the Checking with Addition page using the compact paper-and-pencil method. See Figure 7. Then ask another student to show the same trades with base-ten pieces. See Figure 7.
Ask questions similar to the following to discuss how the two solutions are connected:
- What base-ten pieces did [student name] use to represent 1489? (1 pack, 4 flats, 8 skinnies, and 9 bits)
- When [student name] subtracted 597, were any trades made? (yes, two)
- Explain the trades. (1 flat was traded for 10 skinnies, and 1 pack was traded for 10 flats.)
- How were the trades shown on [student name]'s paper-and-pencil solution? (Possible response: The 8 in the tens column was regrouped as 18, and the 4 in the hundreds column was regrouped as a 3. Then we had to trade again, so the 1 in the thousands column was regrouped as 0, and the 3 in the hundreds column was regrouped as 13.)
- Show how to check this problem with addition. (Add the answer 892 to 597. I get 1489, the number I started with, so I know that I am correct.)
- Think about other subtraction strategies you have used. Do you like this paper-and-pencil method? Why or why not?
Ask students to complete the Subtraction Checkup Assessment Master independently.
Use the Subtraction Checkup Assessment Master with Feedback Box to assess students' progress toward applying place value concepts to make connections among representations of numbers [E1]; subtracting multidigit numbers using mental math strategies [E3]; and using the compact paper-and-pencil method to subtract [E4].
The Workshop in Lesson 5 provides targeted practice.
