Add and subtract three-digit numbers using place value — one column at a time!
When adding or subtracting three-digit numbers, we work column by column from right to left: ONES first, then TENS, then HUNDREDS. If a column adds up to 10 or more, we REGROUP (carry) to the next column. If a column is too small to subtract, we REGROUP (borrow) from the column to the left.
347 + 215 ───── Ones: 7 + 5 = 12 → write 2, carry 1 Tens: 4 + 1 + 1(carried) = 6 → write 6 Hundreds: 3 + 2 = 5 → write 5 Answer: 562
583 − 241 ───── Ones: 3 − 1 = 2 Tens: 8 − 4 = 4 Hundreds: 5 − 2 = 3 Answer: 342 (no regrouping needed here!)
Steps for column addition:
What is 456 + 327?
Remember This!
Always line up your digits carefully before you start. Misaligned columns are the #1 cause of mistakes in three-digit addition and subtraction!