Numbers larger than one thousand are usually added and subtracted in columns: ones under ones, tens under tens, and so on. You start in the ones place; if the sum of two digits is greater than 9, you write only the ones digit of the result and carry the tens to the next column. When subtracting, if the digit on top is smaller, regroup (borrow) from the next place to the left.
This lesson uses five-digit examples with carrying and regrouping; you can open the step-by-step work at the bottom.
Line up the same places in one column
Addition: carry when a column sums to 10 or more
Subtraction: regroup when the top digit is smaller
Check: compare your answer digit by digit with the result
Column addition
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