Let's review what you've learned about numbers in column subtraction. There's a new kind of regrouping (borrowing) when we are subtracting numbers with the digit zero. The rule is that you can't borrow from a zero. What do you do? You have to regroup from the first place value that does not have a zero. When you regroup from a number, you cross it out and rewrite it. Then you can subtract. For example:
We have to regroup to work with the ones place (ones column) in the example above. But since we can't borrow from a zero, we have to regroup from the first digit that is not a zero. The tens digit of 202 is zero. We can't borrow from it. We regroup using 20, and we cross out 20 and rewrite it as 19 plus 1 (19 + 1). Place the 1 you regrouped beside the 2 in the ones place. Now you can subtract.
Let's review this next problem step-by-step.
We can't subtract the ones place, so we have to regroup from the next place value. But the tens place (tens column) has the digit zero. We look for the first digit that is not a zero, which is 5. Let's rewrite 50 as 49 plus 1 (49 + 1).
Now we can subtract. Instead of 3, we now have 13 in the ones place, and 13 minus 9 equals 4. Next, we bring down 49, and we finally have our difference (answer), 494.
Let's do another problem.
We need to regroup so we can subtract the ones place. Both tens place and hundreds place (hundreds column) have zeros, so we go to the first digit that is not a zero, which is 6. So let's rewrite 600.
We rewrote 600 as 599 plus 1 (599 + 1). Now we have 17 on the ones place because 10 plus 7 equals 17 (10 + 7 = 17). Now we can subtract.
Our final difference equals 5,999.
