Subtraction: Taking away or removing objects from a group. The result is called the difference. Subtraction within 20 means the numbers involved are 20 or less.
- Identify the starting amount (minuend)
- Identify the amount being taken away (subtrahend)
- Count or use a strategy to find what remains
- Check that the answer makes sense
There were 8 apples on the table initially.
Sarah takes 3 apples.
8 - 3 = 5
3 + 5 = 8, so the answer is correct.
There are 5 apples left on the table.
• Subtraction concept: Taking away objects from a group
• Counting backward: Starting from 8 and counting back 3
• Verification: Adding the result back to check accuracy
Subtraction within 20: Subtraction problems where both the starting number and the result are 20 or less. This includes numbers from 1 to 20.
Tom starts with 12 pencils.
He gives away 7 pencils.
Count back from 12: 12, 11, 10, 9, 8, 7, 6, 5. So 12 - 7 = 5.
7 + 5 = 12, so the answer is correct.
Tom has 5 pencils left.
• Counting backward: Starting from the larger number and counting back
• Subtraction within 20: Both numbers are between 1 and 20
• Verification: Adding the result back to check accuracy
Subtraction within 20: Problems where the minuend (starting number) is 20 or less, and the subtrahend (number taken away) is also 20 or less, with the result being non-negative.
There were 18 flowers in the garden.
9 flowers were picked.
18 - 9 = 9 (using known facts: 9 + 9 = 18)
9 + 9 = 18, so the answer is correct.
There are 9 flowers still in the garden.
• Known facts: Using addition facts to solve subtraction (9 + 9 = 18, so 18 - 9 = 9)
• Subtraction within 20: Both numbers are between 1 and 20
• Verification: Adding the result back to check accuracy
Choose the strategy that works best for the problem type
Apply the chosen strategy systematically
Add the result back to check the answer
Students develop multiple approaches to solve subtraction problems
Solve each problem using the suggested strategy
Verify each answer by adding back
Check that all answers are correct
Students gain fluency with subtraction within 20
Subtraction: Taking away or removing objects from a group
Minuend: The number being subtracted from
Subtrahend: The number being subtracted
Difference: The result of subtraction
- Identify: Find the starting amount and what is taken away
- Choose: Select an appropriate subtraction strategy
- Solve: Carry out the subtraction
- Verify: Check the answer by adding back
Grade 1 Focus: Developing fluency with subtraction facts up to 20
Problem Solving: Using subtraction to solve real-world problems
Mathematical Reasoning: Understanding the relationship between addition and subtraction
- Concrete materials: Use objects, counters, or manipulatives
- Visual representations: Draw pictures or use number lines
- Fact families: Connect addition and subtraction facts
- Practice: Regular practice with varied problems
• Subtraction concept: Taking away objects from a group
• Within 20 limit: All numbers involved are 20 or less
• Verification: Always add the result back to check
• Strategy flexibility: Use different methods for different problems
Questions & Answers
Question: How can I help Grade 1 students understand subtraction when they confuse it with addition?
Answer: To help students distinguish subtraction from addition:
- Use concrete language: "take away" for subtraction, "add to" for addition
- Emphasize the action: subtraction removes items, addition combines them
- Use visual aids showing items being removed for subtraction
- Practice with word problems that clearly indicate the operation needed
Create anchor charts with clear visual cues and language. Practice both operations side by side to highlight the differences in actions and results.
Question: What are effective strategies for helping students subtract larger numbers from smaller numbers within 20?
Answer: For subtraction within 20, focus on these strategies:
- Counting backward from the larger number
- Using known addition facts (if 7 + 5 = 12, then 12 - 7 = 5)
- Using a number line to visualize the subtraction
- Breaking the subtraction into smaller steps
For example, for 13 - 8, think "what number added to 8 makes 13?" The answer is 5, so 13 - 8 = 5. This builds on known addition facts.
Question: How can I help students who struggle with counting backward for subtraction?
Answer: For students struggling with counting backward:
- Start with smaller numbers and gradually increase difficulty
- Use number lines or hundreds charts for visual support
- Practice counting backward as a separate skill first
- Use the "think addition" strategy (what number added gives the original?)
Provide manipulatives for hands-on practice. Allow students to use their fingers or other tools until they develop fluency. Emphasize the connection between addition and subtraction facts.
This summary provides a complete overview of subtraction within 20 for Grade 1 students, covering all essential elements for effective learning and mastery.
Minuend: The number being subtracted from (the starting amount).
Subtrahend: The number being subtracted (the amount taken away).
Difference: The result of subtraction (what remains).
Within 20 Limit: All numbers involved are 20 or less.
Verification: Always add the result back to check the answer.
Strategy Flexibility: Use different methods for different problems.
Verification: Minuend = Difference + Subtrahend
Intermediate: 12 - 7 = 5 (think: 7 + 5 = 12)
Complex: 18 - 9 = 9 (use known fact: 9 + 9 = 18)
Advanced: 16 - 8 = 8 (double fact recognition)
Visual Help: Use drawings, number lines, or manipulatives
Fact Families: Use addition facts to solve subtraction
Verification: Always add the result back to check accuracy
Mistake 2: Counting forward instead of backward
Mistake 3: Forgetting to verify answers
Mistake 4: Getting confused with larger numbers within 20
- Always identify what you start with and what is taken away
- Use multiple strategies: counting back, addition facts, visual aids
- Verify answers by adding the result back to the subtrahend
- Practice regularly to build fluency with facts up to 20
- Connect addition and subtraction facts for deeper understanding