Grade 2/Addition
Adding whole tens (4 addends, missing) (214)
Solve 4‑addend tens sums with one missing addend.
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Teaching Notes
Most challenging in this series. Students must add three numbers mentally, then find the difference. Break into steps: 1) Identify and add the three known numbers, 2) Subtract from total to find missing number, 3) Check by adding all four.
Vocabulary
Missing addend: A number in an addition problem that is unknown.
Total: The sum of all numbers.
Common Mistakes
- Attempting to add all at once
- Subtracting wrong numbers
- Forgetting to verify answer
- Getting overwhelmed by four numbers
- Incorrectly summing the known addends
- Forgetting to subtract the sum of known addends from the total
- Errors in mental subtraction when finding the missing number
Differentiation
SupportProvide hundreds charts or base ten blocks to visualize adding multiples of ten. Break down the problem into two steps: sum known numbers, then subtract from the total. Work with fewer addends first (2-3).
ChallengeChallenge students to create their own missing addend problems with multiples of ten. Introduce larger sums (e.g., within 1000) or problems with a missing addend in different positions.
Discussion Questions
- How does knowing your tens facts help you solve these problems?
- What strategy do you use to find the missing number?
- How is this problem similar to finding a missing part of a whole?
Extension Activities
- Find missing addends with hundreds.
- Use 5 addends.
- Create your own problems.
Parent Tip
Give your child a total and some parts; ask them to find the missing part.
Learning Path
Skill Cluster
Number Sense & Operations
Estimated Time
15 minutes
Skills Practiced
finding missing addendssubtraction within 1000addition properties
Prerequisites
- Adding multiples of ten (2-3 addends)
- Solving for missing addends within 100
- Understanding the relationship between addition and subtraction
Next Steps
- Adding two-digit numbers with regrouping
- Missing addends with two-digit numbers (full range)
- Solving multi-step addition and subtraction problems