Regrouping to Add Two-Digit Numbers
When adding two-digit numbers, regrouping means trading 10 ones for 1 ten so the math stays correct.
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Regrouping (sometimes called carrying) is what you do when the ones digits in an addition problem add up to 10 or more. You take those extra ones, bundle them into a new ten, and move that ten over to the tens column. This keeps every column with only a single digit in the answer.
Remember the rule
If the ones add up to 10 or more, write the ones digit in the ones column and carry the 1 to the tens column.
Key words
- Ones place
- The far-right spot in a number that tells how many single units there are (the 4 in 24).
- Tens place
- The second spot from the right that tells how many groups of ten there are (the 2 in 24).
- Regroup
- To trade 10 ones for 1 ten so you can keep adding correctly.
- Carry
- Another word for regrouping — you carry the extra ten over to the tens column.
- Sum
- The answer you get when you add two or more numbers together.
- Digit
- Any single number symbol from 0 to 9.
- Column
- A up-and-down line of numbers lined up by place value when you write an addition problem.
- Place value
- The value of a digit based on where it sits in a number — ones, tens, hundreds, and so on.
Worked examples
27 + 35 = ?
→ Step 1: Add the ones: 7 + 5 = 12. Write 2 in the ones place, carry 1 ten to the tens column. Step 2: Add the tens: 1 (carried) + 2 + 3 = 6. Write 6 in the tens place. Answer: 62. · The ones added up to 12, which is more than 9, so regrouping was needed.
48 + 26 = ?
→ Step 1: Add the ones: 8 + 6 = 14. Write 4 in the ones place, carry 1 ten. Step 2: Add the tens: 1 (carried) + 4 + 2 = 7. Write 7 in the tens place. Answer: 74. · Always add the carried 1 first before adding the tens digits.
53 + 19 = ?
→ Step 1: Add the ones: 3 + 9 = 12. Write 2 in the ones place, carry 1 ten. Step 2: Add the tens: 1 (carried) + 5 + 1 = 7. Write 7 in the tens place. Answer: 72.
36 + 47 = ?
→ Step 1: Add the ones: 6 + 7 = 13. Write 3 in the ones place, carry 1 ten. Step 2: Add the tens: 1 (carried) + 3 + 4 = 8. Write 8 in the tens place. Answer: 83.
64 + 22 = ?
→ Step 1: Add the ones: 4 + 2 = 6. No regrouping needed. Step 2: Add the tens: 6 + 2 = 8. Answer: 86. · When the ones add up to 9 or less, you skip regrouping entirely.
75 + 18 = ?
→ Step 1: Add the ones: 5 + 8 = 13. Write 3 in the ones place, carry 1 ten. Step 2: Add the tens: 1 (carried) + 7 + 1 = 9. Write 9 in the tens place. Answer: 93.
Common mistakes
- Forgetting to add the carried 1 to the tens column — this is the most common error.
- Writing both digits of the ones sum (like writing 12 in the ones column instead of just 2 and carrying the 1).
- Carrying a 1 even when the ones digits add up to less than 10 — you only regroup when the sum is 10 or more.
- Adding the tens column before finishing the ones column — always start with the ones first.
- Misaligning digits when writing the problem vertically, which mixes up the ones and tens columns.
FAQs
Why do we always start adding from the ones column?
Because if the ones add up to 10 or more, you need to carry a ten over to the tens column. If you started with the tens, you would not know yet whether an extra ten is coming from the ones.
What does the little 1 written above the tens column mean?
That little 1 is the ten you carried over from the ones column. It means the ones digits added up to 10 or more, so you bundled 10 ones into 1 ten and moved it there.
How do I know when I need to regroup?
Add the ones digits. If the answer is 10 or more, you need to regroup. If it is 9 or less, you do not need to regroup.
Can I use base-ten blocks to help understand regrouping?
Yes! Use small unit cubes for ones and long rods for tens. When you collect 10 unit cubes, trade them in for one rod. That physical trade is exactly what regrouping means.
Is regrouping the same as borrowing?
Borrowing is a word used in subtraction. Regrouping and carrying are the words used in addition. They are related ideas but happen in different operations.
What if both the ones and the tens columns need regrouping?
In second grade you mostly work with two-digit numbers where only the ones column regroups. But the same rule applies to any column: if the sum in a column is 10 or more, write the ones digit and carry the 1 to the next column to the left.
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