# Lesson 18

Standard Algorithm to Add and Subtract

### Lesson Purpose

The purpose of this lesson is to add and subtract large numbers within 100,000 using the standard algorithm.

### Lesson Narrative

In grade 3, students found sums and differences within 1,000. Students analyzed and used different algorithms based on place value, including the standard algorithm. As students work with larger numbers in grade 4, they recognize that the standard algorithm is a reliable and efficient way to add and subtract within 1,000,000.

Grid paper should be made available but not required, as a tool to support aligning digits when adding and subtracting in each activity.

• Representation
• MLR2

### Learning Goals

Teacher Facing

• Add multi-digit numbers, with composing, using the standard algorithm.
• Subtract multi-digit numbers, without decomposing, using the standard algorithm.

### Student Facing

• Let’s find sums and differences of large numbers.

### Required Materials

Materials to Gather

### Lesson Timeline

 Warm-up 10 min Activity 1 15 min Activity 2 20 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

What strategies from earlier grades did students rely on to find sums and differences in the warm-up and first activity, before the standard algorithm was explicitly mentioned? How can you support students in connecting these strategies to the standard algorithm?

### Suggested Centers

• Tic Tac Round (3–5), Stage 2: Any Place (Addressing)
• Number Puzzles: Addition and Subtraction (1–4), Stage 6: Beyond 1,000 (Addressing)

### Print Formatted Materials

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