Grade 1 · Operations & Arithmetic
Add and Subtract Within 20
Learn to choose between addition and subtraction and explain why through clear explanations, worked examples, an interactive model, and guided practice.
Lesson coverage
Learn the whole topic, not just one problem type.
This lesson and its practice bank deliberately rotate across these core facets so students build a connected understanding of the subject.
Decide whether addition or subtraction fits a situation.
Calculate accurately.
Solve equations with a missing quantity.
Translate stories into operations.
Use inverse operations and estimation.
Build the idea
Add and Subtract Within 20 is part of the develop addition/subtraction strategies, place value to 100, measurement, data, and shape reasoning. Start by identifying what each quantity, symbol, diagram, or graph represents before calculating.
Choose the operation
Decide whether addition or subtraction fits a situation. Use a representation that fits the idea, connect it to the relevant mathematical relationship, and explain how the representation supports the result.
Fluency
Calculate accurately. Use a representation that fits the idea, connect it to the relevant mathematical relationship, and explain how the representation supports the result.
Unknown values
Solve equations with a missing quantity. Use a representation that fits the idea, connect it to the relevant mathematical relationship, and explain how the representation supports the result.
Word problems
Translate stories into operations. Use a representation that fits the idea, connect it to the relevant mathematical relationship, and explain how the representation supports the result.
Check & explain
Use inverse operations and estimation. Use a representation that fits the idea, connect it to the relevant mathematical relationship, and explain how the representation supports the result.
Use a reliable strategy
Identify the quantities, choose the operation that matches the situation, calculate carefully, and check whether the result is reasonable.
Check and explain
A correct answer is only part of mathematical understanding. Check units, signs, scale, and whether the result makes sense. Then explain the relationship in words so you can recognize the same structure when the numbers or context change.
Key terms
Words to know
- Add and Subtract Within 20
- The central skill or relationship explored in this lesson.
- Operation
- A mathematical action such as addition or subtraction.
- Inverse operations
- Operations that undo each other.
- Estimate
- A nearby value used to check reasonableness.
Interactive math lab
Change it. See it. Understand it.
Adjust the values and watch the relationship respond.
| Quantity A | 6 |
|---|---|
| Quantity B | 3 |
| Product / area | 18 |
Worked examples
See the idea in action.
The sum is 7.
The inverse subtraction statement recovers one addend from the sum.
Guided practice
20 questions drawn from a 150-question lesson bank.
Each practice session mixes the major skills in this lesson so you practice the whole topic, not just one repeated problem type.
Which expression represents 4 more than 6?
Curriculum reference
Built as a continuous K–12 progression.
The sequence follows widely used K–12 mathematics progressions and references the Common Core mathematics framework. Explanations, examples, interactive models, and practice questions are original FreeLearnHub material.