Adding Columns of Numbers with Regrouping
Adding columns of numbers with regrouping is a Grade 4 skill in Saxon Math Intermediate 4 Chapter 2 that extends carrying to situations where the ones column sums to 20 or more. When three or more numbers are added and their ones digits total 24, for example, students write the ones digit (4) and carry the tens digit (2) to the tens column—not just a 1. For example, adding 48, 15, and 29 produces a ones sum of 22, so 2 is written and 2 is carried. This rule prevents the habit of always carrying just one.
Key Concepts
New Concept When the sum of the digits in the ones column is 20 or more, we move a group of two or more tens to the tens column.
What’s next Next, you'll apply this regrouping skill to add columns of numbers and solve problems involving money.
Common Questions
What happens when the ones column adds up to more than 19 in column addition?
You write the ones digit of the sum in the answer and carry the tens digit to the tens column. For example, if the ones total is 24, write 4 and carry 2.
How do I add 48, 15, and 29 in a column?
Add the ones: 8 plus 5 plus 9 equals 22. Write 2 and carry 2 to the tens column. Add tens: 2 plus 4 plus 1 plus 2 equals 9. Total is 92.
Why should I not always carry just the number 1?
Carrying 1 is only correct when the ones sum is between 10 and 19. If the sum is 22, you carry 2. Always carry the actual tens digit of your sum.
Does the same rule apply when the tens column produces a large sum?
Yes. If adding the tens column (plus any carry) produces a two-digit number, write the ones digit of that sum and carry the tens digit to the hundreds column.
How does this skill connect to later math?
Accurately carrying multi-digit values is essential for multi-digit multiplication, adding money totals, and maintaining precision in all computational work.