Missing Addend: Whole Hundreds Addition

Teaching Notes

Applies subtraction thinking to find missing addends. Two strategies: 1) Count up by hundreds (300, 400, 500... to 800), or 2) Subtract (800 - 300 = 500). Both develop number sense and inverse operation understanding.

Vocabulary

Addend: A number added to another number.

Sum: The result of adding numbers.

Common Mistakes

• Subtracting in wrong direction
• Counting from zero instead of from first number
• Wrong number of zeros in answer
• Not checking answer by adding back
• Forgetting place value (e.g., 200 + __ = 500, answer is 3, not 300).
• Confusing operations (adding instead of subtracting, or vice versa).
• Errors in mental arithmetic when counting on or back by hundreds.

Differentiation

Discussion Questions

• How can we use subtraction to find a missing number in an addition problem?
• What strategies can you use to quickly add or subtract hundreds mentally?
• How is adding whole hundreds similar to adding single-digit numbers?

Extension Activities

• Count by hundreds forward.
• Count by hundreds backward.
• Find missing hundreds.

Parent Tip

Ask your child to count by hundreds from a starting number to a target number.

Skill Cluster

Number Sense & Operations

Estimated Time

15 minutes

Skills Practiced

Prerequisites

• Adding/Subtracting within 100
• Place Value: Understanding Hundreds
• Relationship between Addition and Subtraction

Next Steps

• Adding/Subtracting Whole Hundreds (2-step problems)
• Adding 3-Digit Numbers (No Regrouping)
• Subtracting 3-Digit Numbers (No Regrouping)
• Adding whole tens (missing addend)
• Subtracting whole hundreds
• Adding 3-digit numbers (no regrouping)