Main content

## Subtracting with regrouping within 1000

## Video transcript

Let's try to subtract
164 from 301, and I encourage you
to pause this video and try it on your own first. So let's go place
by place, and we can realize where we have to do
some borrowing or regrouping. So in the ones place,
we have an issue. 4 is larger than 1. How do we subtract a larger
number from a smaller number? We also an issue
in the tens place. 6 is larger than 0. How do we subtract 6 from 0? So the answer that might
be jumping into your head is oh, we've got to do some
borrowing or some regrouping. But then you might be
facing another problem. You'd say, OK, well, let's try
to borrow from the tens place here. So we have a 1. If we could borrow 10 from the
tens place, it could be 11. But there's nothing
here in the tens place. There's nothing to
borrow, so what do we do? So the way I would
tackle it is first borrow for the tens place. So we have nothing here,
so let's regroup 100 from the hundreds place. So that's equivalent
to borrowing a 1 from the hundreds place. So that's now a 2. And now in the tens
place, instead of a 0, we are going to have a 10. Now, let's make sure that
this still makes sense. This is 200 plus 10 tens. 10 tens is 100, plus 1. 200 plus 100 plus
1 is still 301. So this still makes sense. Now, the reason why
this is valuable is now we have something to
regroup from the tens place. If we take one of these tens,
so now we're left with 9 tens, and we give it to the ones
place, so you give 10 plus 1, you're going to be left with 11. And we can verify that
we still haven't changed the value of the actual number. 200 plus 90 is 290,
plus 11 is still 301. And what was neat about
this is now up here, all of these numbers are larger
than the corresponding number in the same place. So we're ready to subtract. 11 minus 4 is-- let's see, 10
minus 3 is 7, so 11 minus 4 is 7. 9 minus 6 is 3,
and 2 minus 1 is 1. So we are left with 137.