Grade 2/Addition
Adding whole tens (209)
Practice adding two whole tens (multiples of 10) to build fast mental addition with tens.
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Teaching Notes
This activity builds fluency in adding multiples of 10, a foundational mental math skill for second graders. Emphasize the connection between basic addition facts (e.g., 3+4=7) and adding tens (30+40=70) through place value understanding.
Vocabulary
Whole tens: Numbers like 10, 20, 30, etc.
Add: To combine numbers.
Common Mistakes
- Forgetting the zero when adding tens (e.g., 30+40=7).
- Treating tens as ones (e.g., confusing 3 tens + 4 tens with 3 ones + 4 ones).
- Difficulty transferring single-digit addition knowledge to tens.
Differentiation
SupportUse concrete manipulatives like base ten blocks or a number line to visualize adding groups of ten. Provide a reference chart for counting by tens.
ChallengeChallenge students to add three multiples of ten or to add a multiple of ten to a two-digit number (e.g., 25 + 30). Encourage explaining their mental strategies.
Discussion Questions
- How is adding 20 + 60 similar to adding 2 + 6?
- Why is understanding place value important when adding tens?
- When might you use mental math to add tens in real life?
Extension Activities
- Use a number line to skip count by tens.
- Create addition stories with tens.
- Play with base-ten blocks.
Parent Tip
Use coins like dimes to represent tens and practice adding them.
Learning Path
Skill Cluster
Number Sense & Operations
Estimated Time
15 minutes
Skills Practiced
adding whole tensskip counting by tensplace value tens
Prerequisites
- Counting by tens to 100
- Understanding place value (tens and ones)
- Basic single-digit addition facts (sums to 10)
Next Steps
- Adding a multiple of ten to a two-digit number (e.g., 34 + 20)
- Adding two-digit numbers without regrouping
- Estimating sums within 100