Let's trade (regrouping to subtract)

This word (trade) will introduce regrouping to subtract by allowing students to "trade" manipulatives to regroup.

A lesson plan for grades 1–2 Mathematics

By Sarah Cole

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Related topics

• Learn more about arithmetic, hands-on, mathematics, and subtraction.

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Learning outcomes

Students will identify when it is necessary to group to subtract. They will also use manipulatives to regroup and learn to how to show they have regrouped on paper.

Teacher planning

Time required for lesson

1 hour

Materials/resources

• bags of unifix cubes
• paper with four subtraction problems (regrouping required)

Pre-activities

• Students should know subtraction facts to 18.
• Students should know two-digit subtraction without regrouping.
• Students should be familiar with place value (ones and tens) and base ten blocks.
• The teacher should have established rules for working with partners and manipulatives.

Activities

1. Write a subtraction problem on the board (no regrouping). Ask for volunteers to explain how to solve the problem.
2. Using unifix cubes (some linked together) as you would base ten blocks, model the subtraction problem.
3. Repeat 1 and 2 several times.
4. Present the class with a challenge. Write a problem on the board that requires regrouping. Ask students to think of ways to solve that problem. Point out strong and weak points of ideas using questioning.
5. Show students that they could take ten ones from the tens place and add them to the ones place. Break the blocks apart and count to see that you still have the same number of blocks. Show correct notation for doing this on the board. Recount the number of ones and tens blocks.
6. Demonstrate that the subtraction process remains the same.
7. Repeat steps 4-6 several times until students can explain the process without much assistance.
8. Ask two students to come to the front of the room. Give one student a set of unifix cubes and record that number on the board.
9. Tell the student that you would like them to “take away” a given number of blocks and give them to the other student. Record this number. You should now have a subtraction problem that requires regrouping.
10. Ask the class for volunteers to help the students figure out what to do.
11. Use questioning to guide the students through the correct process (trade with the tens, cross out the number, write one less, add to the ones, cross out the number, add ten more, subtract ones, subtract tens).
12. Complete steps 8-11 several times.
13. Explain to students that they will be given a bag of unifix cubes and a partner. They should get a pencil and together do the four problems on the paper you are giving them.
14. Use your method of deciding who goes first to decide who will hold the blocks the first time and who will be given blocks.
15. Monitor student work.
16. After completing assignment, students should return to the group. As a group, review the problems.

Assessment

In a math journal, students should tell with words or pictures how they would solve this problem: 32-17. Check explanations for understanding.