See exactly how borrowing (regrouping) works, column by column
Column subtraction is the standard written method for subtracting one number from another. You line the numbers up vertically so that digits with the same place value are in the same column, then work from right to left — subtracting the bottom digit from the top digit in each column in turn.
When the top digit in a column is smaller than the bottom digit, you can't subtract directly. You borrow 1 from the next column to the left — reducing that digit by 1 — and add 10 to the current column's top digit. Borrowing is the most confusing part of subtraction for many students, which is exactly why Unfold Math shows each borrow with a clear animation.
If the digit you need to borrow from is itself a zero, you can't take 1 from it directly. You have to look further left and borrow from the first non-zero digit you find, passing the borrow through each zero column along the way — each of those zeros becomes a 9 in the process.
Always write the larger number on top. Work column by column from right to left, and every time you borrow, immediately update the digit in the column you borrowed from before moving on. Check your answer by adding the result back to the number you subtracted: you should always get the original top number.
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