Grade 2/Addition
Adding whole tens (missing number) (210)
Find the missing whole tens addend to complete each sum.
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Teaching Notes
This collection helps students practice finding missing addends when working with whole tens. Encourage them to use place value understanding by relating problems like 30 + ? = 80 to 3 + ? = 8. Use base-ten blocks or ten-frames to visualize the addition of tens.
Vocabulary
Missing addend: A number in an addition problem that is unknown.
Sum: The result of adding numbers.
Common Mistakes
- Not recognizing tens as units (e.g., treating 30 as 3 ones instead of 3 tens)
- Basic addition errors when finding the related single-digit sum
- Confusion with inverse operations (subtraction) to find the missing addend
Differentiation
SupportProvide manipulatives like base-ten blocks or ten-frames. Explicitly connect to single-digit addition facts (e.g., if 3 + 5 = 8, then 30 + 50 = 80).
ChallengeIntroduce problems with three whole tens addends, or extend to missing minuends/subtrahends with whole tens. Challenge with missing addends in sums beyond 100.
Discussion Questions
- How is adding tens similar to adding ones?
- What strategy did you use to find the missing number?
- Can you use subtraction to help find the missing addend? How?
Extension Activities
- Use fact families to solve.
- Draw pictures to represent problems.
- Play 'guess the number'.
Parent Tip
Use objects to show a total and ask how many are missing to reach it.
Learning Path
Skill Cluster
Number Sense & Place Value
Estimated Time
15 minutes
Skills Practiced
missing addend whole tenssubtraction as inversefinding unknown addends
Prerequisites
- Counting by tens
- Place value (tens and ones)
- Addition within 20
Next Steps
- Subtracting whole tens
- Adding two-digit numbers (no regrouping)
- Missing addends with two-digit numbers