Welcome to the presentation on level 4 subtraction.
Let's get started with some problems.
First problem I have here is 33,220 minus 399.
So this like we did with, I believe, that we also did
borrowing in the level subtraction, we have to go
through all of the digits in the top number starting with
the top right digit and make sure that they are larger
than the digit below it.
Because you can only attract a smaller number from
a larger number.
You can't do it the other way, at least, until we
learn negative numbers.
So let's go through this and check to make sure all the
top numbers are larger.
Well immediately, we see no.
Well this 0 is not larger than 9.
So we have to borrow to make the 0 bigger.
So what we do is we borrow 1-- well some people say
we're borrowing a 1.
Some people say, I mean, borrowing a 1 from the
10's place is really like borrowing a 10.
So for simplicity let's just say we're borrowing a 1.
So you borrow a 1 from this 2 and this 10 will become a-- the
0 sorry, will become a 10.
And since we borrowed that 1, this 2 will become a 1.
We took 1 away from this 2 and we gave it to the 0 to make 10.
We actually took 10 away from this 2 because this
2's in the 10's place.
I don't want to confuse you too much.
If just the mechanics of it are we took 1 away from the 2 and
we put it in front of the 0 to make 10.
Now let's keep checking.
So now we have a 1 in this place.
1 is smaller than 9, so we have to borrow again.
So we borrow 1 from this 2 now.
So this 2 now becomes 1.
And this 1 will now become an 11.
So now we have a 10 is larger than a 9.
11 is larger than a 9.
1 is not larger than 3, so we have to borrow again.
This is a good problem.
Maybe I should've warmed you all up a little bit more.
It involves a lot of borrowing.
So in order to borrow we do the same thing over again.
This 1 will become 11.
And it's going to borrow from this 3, which will become a 2.
I think we're done now.
10 is larger than 9, 11 is larger than 9, 11 is larger
than 3, 2 is larger than nothing, 3 is larger
than nothing.
So now we're ready to subtract.
This is the easy part.
10 minus 9 is 1.
11 minus 9 is 2.
11 minus 3 is 8.
2 minus nothing is 2.
3 minus nothing is 3.
So we get 32,821.
The only thing that makes this harder than just normal
subtraction is that you have to know how to do the borrowing.
And the way I do the borrowing might be different than the way
you learned in school, but I think it's easier because you
do all of the borrowing at once instead of switching back and
forth between borrowing and subtracting.
So all we did here, we said that 0 is less than 9.
Let's borrow 1.
The 0 becomes a 10 because we got this 1 right here.
We got this 1 from this 2 and this 2 became a 1.
I think you might see the pattern if we do a couple
of more problems.
So let's do a couple of more.
If I had 25,633 minus 578.
So name drill.
Start at the top right and we make sure that the digits on
top are larger than the digit below it.
Immediately we see 3 is smaller than 8, so we have to borrow.
So this 3 will become 13.
And then we borrow from this 3, which will now become 2.
We took a 1 away from this 3, it became a 2, and
this 1 is right here.
13 is now larger than 8, but 2 is now smaller than 7.
So we have to borrow again.
This 2 becomes a 12.
And this 6 will become a 5.
13 is larger than 8, 12 is larger than 7, 5 is the same
as 5, so you can actually do the subtraction.
Because 5 minus 5 is 0.
As long as the top number's not smaller than the
number below it.
And then obviously this 5 is larger than this 0 and
this 2 is larger than this nothing here.
So now we're ready to subtract.
13 minus 8 is 5.
12 minus 7 is 5.
5 minus 5 is 0.
5 minus nothing is 5.
Bring down the 2.
So the answer is 25,055.
So let's do a problem now that I think will confuse you a
little bit more because the borrowing isn't as easy.
You have to actually borrow from a couple places.
Let's say I had 37,002 minus-- let's say I had 155.
So the same drill.
So this 2 is less than 5, so we have to borrow.
So this 2 will become a 12.
But huh, there's a 0 here, so you can't borrow from the 0.
Some people will let you borrow from the 0, but I think that
just confuses things because you can't borrow from the
0, there's nothing there.
So instead of borrowing from the 0 we look to this 0.
Well, there's still nothing there.
So now we look, oh, there's a 7 here.
So what we do is instead of borrowing a 1 from the 0, which
is hard to do, we borrow 1 from this 700, from this whole 700.
And what is 700 minus 1?
Right, it's 699.
So that 700 becomes 699.
Cross all of this out.
And now let's check our numbers again.
12 is larger than 5, nine is larger than 5, 9 is larger than
1, 6 is larger than nothing, and 3 is larger than nothing,
so we're ready to subtract.
12 minus 5 is 7.
9 minus 5 is 4.
9 minus 1 is 8.
6 minus nothing is 6.
3 minus nothing is 3.
So there, we're done.
The answer is 36,847.
I think we could have time for one more problem.
Let's say I had 3,201 minus-- let's say it's 502.
Same drill.
1 is less than 2, so we have to borrow.
Turn that into an 11.
But you can't borrow from the 0, so you're going to have to
borrow from this entire 20.
Well, what's 20 minus 1?
Right, it's 19.
This becomes a 19.
So let's check again.
11 is greater than 2.
Check.
9 is greater than 0.
Check.
Uh-oh.
1 is not greater than 5.
So we have to borrow again.
This 1 becomes an 11.
We borrowed from this 3, which becomes a 2.
11 is greater than 2, 9 is greater than 0, 11 is greater
than 5, 2 is obviously greater than nothing below it.
So we're ready to subtract.
11 minus 2 is 9.
9 minus 0 is 9.
11 minus 5 is 6.
And 2 minus nothing is 2.
So 3,201 minus 502 is equal to 2,699.
I think you're now ready to try some of the level 4
subtraction problems.
You just always have to remember, do you're
borrowing first.
Make sure all the numbers on top are larger than, or at
least as large as all the numbers on the bottom.
And then you can just do your subtraction like a normal
subtraction problem.
I hope you have some fun doing this.
Talk to you later.