Addition is combining two or more numbers to find their total. When adding three-digit numbers, we work from right to left, starting with the ones place.
Step-by-step process:
Always remember to add any carried-over numbers to the next column. Keep your work neat by writing numbers in straight columns.
Subtraction is finding the difference between two numbers. When subtracting three-digit numbers, we also work from right to left, but sometimes we need to regroup.
Step-by-step process:
Regrouping means borrowing from the next higher place value. Cross out the original number and write the new value above it.
Sometimes when adding, we need to regroup in multiple places. This happens when the sum in any column is 10 or greater.
Step-by-step process:
When the sum in any column is 10 or more, write the ones digit and carry the tens digit to the next column.
Subtracting when there are zeros in the number requires special regrouping. We may need to regroup across multiple columns.
Step-by-step process:
When regrouping across zeros, remember that 500 is the same as 4 hundreds, 9 tens, and 10 ones.
Good mathematicians always check their work. For addition, use subtraction to verify. For subtraction, use addition to verify.
Checking addition: If 148 + 235 = 383, then 383 - 235 should equal 148
Checking subtraction: If 524 - 367 = 157, then 157 + 367 should equal 524
Checking your work helps catch mistakes and builds confidence in your answers. Make it a habit!