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Welcome to the presentation on level 4 subtraction.

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Let's get started with some problems.

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First problem I have here is 33,220 minus 399.

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So this like we did with, I believe, that we also did

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borrowing in the level subtraction, we have to go

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through all of the digits in the top number starting with

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the top right digit and make sure that they are larger

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than the digit below it.

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Because you can only attract a smaller number from

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a larger number.

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You can't do it the other way, at least, until we

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learn negative numbers.

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So let's go through this and check to make sure all the

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top numbers are larger.

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Well immediately, we see no.

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Well this 0 is not larger than 9.

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So we have to borrow to make the 0 bigger.

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So what we do is we borrow 1-- well some people say

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we're borrowing a 1.

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Some people say, I mean, borrowing a 1 from the

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10's place is really like borrowing a 10.

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So for simplicity let's just say we're borrowing a 1.

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So you borrow a 1 from this 2 and this 10 will become a-- the

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0 sorry, will become a 10.

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And since we borrowed that 1, this 2 will become a 1.

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We took 1 away from this 2 and we gave it to the 0 to make 10.

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We actually took 10 away from this 2 because this

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2's in the 10's place.

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I don't want to confuse you too much.

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If just the mechanics of it are we took 1 away from the 2 and

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we put it in front of the 0 to make 10.

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Now let's keep checking.

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So now we have a 1 in this place.

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1 is smaller than 9, so we have to borrow again.

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So we borrow 1 from this 2 now.

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So this 2 now becomes 1.

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And this 1 will now become an 11.

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So now we have a 10 is larger than a 9.

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11 is larger than a 9.

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1 is not larger than 3, so we have to borrow again.

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This is a good problem.

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Maybe I should've warmed you all up a little bit more.

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It involves a lot of borrowing.

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So in order to borrow we do the same thing over again.

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This 1 will become 11.

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And it's going to borrow from this 3, which will become a 2.

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I think we're done now.

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10 is larger than 9, 11 is larger than 9, 11 is larger

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than 3, 2 is larger than nothing, 3 is larger

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than nothing.

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So now we're ready to subtract.

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This is the easy part.

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10 minus 9 is 1.

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11 minus 9 is 2.

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11 minus 3 is 8.

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2 minus nothing is 2.

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3 minus nothing is 3.

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So we get 32,821.

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The only thing that makes this harder than just normal

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subtraction is that you have to know how to do the borrowing.

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And the way I do the borrowing might be different than the way

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you learned in school, but I think it's easier because you

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do all of the borrowing at once instead of switching back and

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forth between borrowing and subtracting.

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So all we did here, we said that 0 is less than 9.

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Let's borrow 1.

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The 0 becomes a 10 because we got this 1 right here.

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We got this 1 from this 2 and this 2 became a 1.

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I think you might see the pattern if we do a couple

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of more problems.

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So let's do a couple of more.

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If I had 25,633 minus 578.

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So name drill.

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Start at the top right and we make sure that the digits on

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top are larger than the digit below it.

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Immediately we see 3 is smaller than 8, so we have to borrow.

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So this 3 will become 13.

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And then we borrow from this 3, which will now become 2.

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We took a 1 away from this 3, it became a 2, and

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this 1 is right here.

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13 is now larger than 8, but 2 is now smaller than 7.

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So we have to borrow again.

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This 2 becomes a 12.

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And this 6 will become a 5.

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13 is larger than 8, 12 is larger than 7, 5 is the same

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as 5, so you can actually do the subtraction.

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Because 5 minus 5 is 0.

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As long as the top number's not smaller than the

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number below it.

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And then obviously this 5 is larger than this 0 and

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this 2 is larger than this nothing here.

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So now we're ready to subtract.

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13 minus 8 is 5.

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12 minus 7 is 5.

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5 minus 5 is 0.

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5 minus nothing is 5.

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Bring down the 2.

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So the answer is 25,055.

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So let's do a problem now that I think will confuse you a

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little bit more because the borrowing isn't as easy.

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You have to actually borrow from a couple places.

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Let's say I had 37,002 minus-- let's say I had 155.

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So the same drill.

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So this 2 is less than 5, so we have to borrow.

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So this 2 will become a 12.

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But huh, there's a 0 here, so you can't borrow from the 0.

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Some people will let you borrow from the 0, but I think that

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just confuses things because you can't borrow from the

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0, there's nothing there.

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So instead of borrowing from the 0 we look to this 0.

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Well, there's still nothing there.

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So now we look, oh, there's a 7 here.

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So what we do is instead of borrowing a 1 from the 0, which

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is hard to do, we borrow 1 from this 700, from this whole 700.

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And what is 700 minus 1?

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Right, it's 699.

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So that 700 becomes 699.

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Cross all of this out.

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And now let's check our numbers again.

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12 is larger than 5, nine is larger than 5, 9 is larger than

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1, 6 is larger than nothing, and 3 is larger than nothing,

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so we're ready to subtract.

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12 minus 5 is 7.

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9 minus 5 is 4.

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9 minus 1 is 8.

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6 minus nothing is 6.

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3 minus nothing is 3.

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So there, we're done.

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The answer is 36,847.

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I think we could have time for one more problem.

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Let's say I had 3,201 minus-- let's say it's 502.

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Same drill.

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1 is less than 2, so we have to borrow.

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Turn that into an 11.

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But you can't borrow from the 0, so you're going to have to

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borrow from this entire 20.

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Well, what's 20 minus 1?

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Right, it's 19.

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This becomes a 19.

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So let's check again.

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11 is greater than 2.

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Check.

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9 is greater than 0.

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Check.

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Uh-oh.

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1 is not greater than 5.

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So we have to borrow again.

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This 1 becomes an 11.

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We borrowed from this 3, which becomes a 2.

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11 is greater than 2, 9 is greater than 0, 11 is greater

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than 5, 2 is obviously greater than nothing below it.

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So we're ready to subtract.

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11 minus 2 is 9.

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9 minus 0 is 9.

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11 minus 5 is 6.

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And 2 minus nothing is 2.

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So 3,201 minus 502 is equal to 2,699.

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I think you're now ready to try some of the level 4

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subtraction problems.

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You just always have to remember, do you're

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borrowing first.

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Make sure all the numbers on top are larger than, or at

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least as large as all the numbers on the bottom.

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And then you can just do your subtraction like a normal

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subtraction problem.

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I hope you have some fun doing this.

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Talk to you later.

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