Adding whole tens

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

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.

Skill Cluster

Number Sense & Operations

Estimated Time

15 minutes

Skills Practiced

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