Base Ten Operations
GradesGrade 1Base Ten OperationsAdding Within 100

Adding Within 100

🔟 Base Ten Operations
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Adding Within 100

Add a two-digit number and a one-digit number — tens stay, ones change!

When you add a two-digit number (like 34) and a one-digit number (like 5), the tens digit usually stays the same — you only add in the ones place. But if the ones add up to 10 or more, you "regroup" (carry over) into the tens!

✏️Adding 34 + 5 (no regrouping)
34 = 3 tens + 4 ones
+ 5 =          + 5 ones
──────────────────────
   = 3 tens + 9 ones = 39

The tens stayed at 3. Only the ones changed: 4 + 5 = 9.
🎒Adding 47 + 6 (with regrouping)
47 = 4 tens + 7 ones
+ 6 =          + 6 ones
──────────────────────
7 + 6 = 13 ones = 1 ten + 3 ones

The extra ten joins the tens place:
4 tens + 1 new ten + 3 ones = 5 tens + 3 ones = 53!

How to add a 2-digit + 1-digit number:

1Add the ones digits together
2If the ones sum is less than 10: write it in the ones place
3If the ones sum is 10 or more: write the ones digit and carry 1 ten
4Add any carried ten to the tens digit
5Write the final tens digit — done!
✏️ Try It!

What is 56 + 7?

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Remember This!

Always add the ONES first. If the ones add up to more than 9, bundle 10 ones into a new ten and carry it over to the tens column!

Practice with CalcVerse
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