Subtraction Across Zeros

Subtraction Across Zeros

When a number has one or more zeros in the middle, you may need to regroup before subtracting. The key idea is that you cannot subtract a larger digit from a smaller one in a place value column, so you borrow from the next nonzero digit to the left.

Method

1. Start at the ones place and compare the top and bottom digits.
2. If the top digit is too small, regroup across the zeros:
   • Move left until you find a digit you can borrow from.
   • Reduce that digit by 1.
   • Turn each zero you pass into 9, because each place is being adjusted.
   • Increase the target place by 10.
3. Subtract each column from right to left.
4. Write the result carefully, keeping place values aligned.

Example idea

If the top number has zeros in the middle, the borrowing may pass through several places before reaching a nonzero digit. Treat each place one step at a time so you do not skip a column.

Check your work

Add your answer to the bottom number. If the sum matches the original top number, your subtraction is correct.

Common mistake to avoid

Do not borrow only from the nearest zero. You must borrow from the first nonzero digit to the left and adjust every place in between.