Direct students' attention to the Subtracting with Base-Ten Pieces pages in the Student Guide. The first two questions show how two students, Kathy and Josh, solved 573 − 289 with base-ten pieces. Students will work with their partners to recreate both solutions with their own base-ten pieces. The third question asks the partners to compare Kathy's and Josh's methods. Assign Questions 1–3 to student pairs.
- How are the methods alike? (They both solve the same problem. They get the same answer. You have to trade a flat for 10 skinnies and a skinny for 10 bits.)
- How are they different? (The first method takes away bits first. The second method takes away flats first.)
- What happens when you're subtracting and you don't have enough bits? (You take one of the skinnies away and trade it for 10 bits. Then you can take away as many bits as you need.)
- What if you don't have enough skinnies? (You can do the same thing—you trade. You can trade 1 flat for 10 skinnies.)
- Does trading change your number? (No. 10 skinnies is the same as 1 flat, so the value of the number stays the same.)
Ask students to tell their partners what they learned. Then have them report to the class what their partners told them. Here are some sample student responses from a classroom video:
“John said he never knew that we could take one of the flats and trade it for skinnies.”
“Well, I learned that instead of a hundred we can trade 10 tens for a hundred. That's the same thing as a hundred.”
Assign Questions 4–10.
Use Check-In: Questions 6–10 on the Subtracting with Base-Ten Pieces pages in the Student Guide to determine students' progress toward applying place value concepts to make connections between representations of numbers and base-ten pieces [E1] and representing and solving multidigit subtraction problems using base-ten pieces [E2].
The Workshop in Lesson 5 provides targeted practice.
