Overview
This lecture reviews how to add three-digit numbers using regrouping (also called carrying), emphasizing proper alignment of place values.
Aligning Place Values
- Always line up numbers so each digit is in the correct column (ones, tens, hundreds).
- Stacking numbers vertically helps ensure correct alignment for addition.
Steps for Three-Digit Addition with Regrouping
- Start adding from the rightmost column (ones place).
- If the sum in a column is 10 or more, regroup by carrying to the next column left.
- Write the ones digit of the sum in that place; carry the tens digit above the next column.
Example Problem Breakdown
- When adding 7 (ones) + 5 (ones), the sum is 12; write 2 in the ones place, carry 1 to the tens.
- Add tens column: carried 1 + 6 + 9 = 16; write 6 in the tens place, carry 1 to the hundreds.
- Add hundreds column: carried 1 + 4 + 2 = 7; write 7 in the hundreds place.
Final Answer
- The sum of the example problem is 762.
Key Terms & Definitions
- Place Value — The value of a digit based on its position (ones, tens, hundreds) in a number.
- Regrouping (Carrying) — Rewriting a sum in one place value as extra value in the next higher place.
- Sum — The result of an addition problem.
Action Items / Next Steps
- Practice more three-digit addition problems with regrouping.
- Review lining up numbers by place value before starting addition.