3-Digit Addition and Subtraction

Even at three digits, the column method still works one place at a time. Addition runs from no carrying up to two carries, subtraction covers no borrowing and one borrow, and the practice centers on fill-in-the-blank items and word problems in forms such as 3-digit plus 2-digit and 3-digit minus 3-digit.

In 3-Digit + 2-Digit (Fill in the Blank), the two-digit number gets written flush with the hundreds column, and the answer is off by 100 or more. When the tens digit is 0 in subtraction, the two-stage borrow from the hundreds is skipped, leaving a 0 or a 9 in that place alone.

The column-calculation procedure, lining up places and starting from the ones digit, is unchanged from the method settled by 2-Digit Subtraction. Only the digit count grows to three here, and this same reasoning carries straight into Column Addition in grade 3, where carrying and borrowing happen more often.