Subtraction With Regrouping

Subtraction with Regrouping

When subtracting multi-digit whole numbers, you may need to regroup if the digit on top is smaller than the digit below it in a place value. Regrouping means taking 1 ten from the next place on the left and turning it into 10 ones, or 1 hundred into 10 tens, and so on.

Method

1. Line up the numbers by place value: ones under ones, tens under tens, hundreds under hundreds.
2. Start at the rightmost column.
3. If the top digit is large enough, subtract normally.
4. If not, borrow/regroup from the next place to the left.
5. Reduce that left digit by 1, and add 10 to the current place.
6. Continue column by column from right to left.

Example idea

If you need to do 42 − 18, the 2 ones cannot subtract 8 ones. Regroup 1 ten from 4 tens, so 42 becomes 3 tens and 12 ones. Then 12 − 8 = 4, and 3 − 1 = 2, giving 24.

Check your work

Add the answer to the number being subtracted. If the result matches the original number, the subtraction is correct.