Multi-Digit Addition and Subtraction

Addition with Regrouping

When digits in a column add up to 10 or more, regroup (carry) to the next column.

Example: $3,456 + 2,789$

Step by step:

• Ones: $6 + 9 = 15$ → write 5, carry 1
• Tens: $5 + 8 + 1 = 14$ → write 4, carry 1
• Hundreds: $4 + 7 + 1 = 12$ → write 2, carry 1
• Thousands: $3 + 2 + 1 = 6$

Answer: $3,456 + 2,789 = 6,245$ ✅

Subtraction with Regrouping

When you can't subtract a digit, borrow from the next column.

Example: $5,302 - 1,847$

• Ones: $2 - 7$ → can't do it! Borrow from tens
• Tens: $0 - 4$ → need to borrow from hundreds too
• Continue borrowing as needed

Answer: $5,302 - 1,847 = 3,455$ ✅

Estimating to Check

Always estimate to check if your answer is reasonable:

• $3,456 + 2,789 \approx 3,500 + 2,800 = 6,300$ ✓ (close to 6,245)

Word Problems

Key words for addition: total, sum, altogether, combined, in all Key words for subtraction: difference, how many more, how much less, remaining

Tip: Always line up numbers by place value when adding or subtracting!