(upbeat music) (animation sounds) - [Children] 'Math Mights'.

- Welcome third graders.

My name is Mrs Ignani, and I'm here for another exciting episode of 'Math Mights'.

Let's check out our plan for today.

First off, we're gonna warm up our brains with a Mystery Math Mistake.

Then we're gonna spend some time subtracting within 1000.

Oh no, third graders!

What's happened to our Mathville characters.

It looks like their strategies are all mixed up.

DC is holding Abracus's wand, what's going on?

Here's how the Mystery Math Mistake works.

First one of our characters from Mathville is going to share with us a problem that they are having a difficult time solving.

It's gonna be our chance to play detectives and closely look at that problem and see if we can find the mistake and then help them correct it.

I wonder which Math Mystery Mathville character needs help today.

T-Pops needs our help.

He tried to solve 364 plus 327 and he got 681.

Let's see if we can take a look at how T-Pops solved this.

You see, I have our equation written out 364 plus 327.

T-Pops told me that he started with his ones and that four plus seven is 11.

He then looked at his tens columns and 60 plus 20 equals 80.

Which left our hundreds, 300 plus 300 equals 600 to get the answer 681.

What do you think boys and girls, did you get the same answer that T-Pops did?

Did you see a Mystery Math Mistake?

Let's see what the boys say.

Landon said, "I don't think T-Pops has the correct answer.

I know because four plus seven doesn't equal one, it is 11."

Looking I see that four plus seven.

Oh, Landon's correct.

We have one here, but we don't have where the other ten is to make 11.

Let's see what Ryan says.

Ryan said, "I think when, T-Pops was adding, he forgot to add his re-group in the tens.

The answer should be 691."

Well, looking at what Ryan is saying, I think he's correct.

We did not have a regroup in the tens.

So we need to fix this problem.

If we have four plus seven equals 11, we need to make sure that we are showing that 10 are one, one and our 10.

So that we can accurately add our tens now, which six tens plus two tens plus one ten is actually nine.

And so double-checking our work, three hundreds plus three hundreds is six.

Our actual answer should be 691.

Remember when we're using T-Pops's strategy, we have to make sure that we are re-grouping correctly.

And we're looking and adding all of those columns the right way.

Let's check out our, "I can" Statement for the Day.

Our I can Statement of the Day, is I can subtract within 1000.

Oh, look, it's Springling.

She has the problem, 428 minus 213 for us to solve by counting up or back on the open number line.

Lets see how Springling would solve this problem today, looking at our problem, 428 minus 213.

I'm gonna go ahead and set this up on an open number line, just like Springling would.

Now my first number is my minuend and my second number is my subtrahend.

And so it's very important that we make sure when we set up these number lines, that we have it in the correct spot.

So my subtrahend is actually going to go towards the beginning of my number line, because that number is actually smaller than the first number.

So it just makes sense that that would go first.

Next, I'm gonna put my minuend towards the end 428.

Now using us, brains.

We know that we are not going to count one by one, and we're actually going to see how far we can count and jump to that decade number.

And we're actually gonna go by hundreds.

So looking in starting at 213, I'm gonna go ahead and count and take that hope to 313 to make Springling happy going a distance of 100.

Next I'm gonna do the same thing and go another hundred to get me to 413.

Again, taking a big jump on my number line, Springling would be so proud.

And next I know that I just have a little bit of a distance to go now that I'm at 413 to get to 428.

So I'm gonna go ahead and use another friendly number.

I'm gonna actually go to 420, do a hop, covering a distance of seven.

And then all I have left is a hop covering the distance of eight to get to 428.

Now we can't forget the last step that Springling loves to do, and that is adding up all that distance to get her total.

So I know right here I have 200 because 100 plus 100 is 200, plus seven plus eight, which equals 215.

So I know that 428 minus 213 equals 215, nice work boys and girls.

That is an excellent strategy to keep in your back pocket as third graders.

But that's not the only strategy that we can use.

Let's see who can help us with our next subtraction problem.

(upbeat music) It's Minnie and Subbie.

Minnie and Subbie are our twins sisters from Mathville and like all sisters, they sometimes don't always get along.

So their parents have told them they need to keep a tails with apart, which makes sense since they have their adjoining tail.

Minnie and Subbie love to work with compensation and their technique uses a shifting number line.

But they have to make sure that when one sister moves, the other sister follows so that their tail stays nice and straight and doesn't drag in the mud.

Let's see how Minnie and Subbie would solve the next subtraction problem.

Looking at the problem that Minnie and Subbie want us to solve today, we have 601 minus 256.

Minnie and Subbie want us to use compensation and shifting that number line to solve it today.

So if I have 601 minus 256, sometimes you'll see that problem set up, where the numbers are stacked 601 minus 256.

But looking, we see that that's not very easy to take away from.

Taking six out of one, you have to re-group and it's just not their style.

Minnie and Subbie do not like re-grouping.

So we're gonna go ahead and use their strategy of shifting the number line.

This is going to be our minuend, whereas our second, is our subtrahend.

Actually that's how Minnie and Subbie got their names.

Let me show you, when you're setting up on a number line, you're always going to put your subtrahend first, because it is the lower number.

So we have Subbie here and we have Minnie over here.

So then looking at our equation, 256 is going to go first on our number line.

While 601 is going to go towards the back of our number line.

Now thinking about Minnie and Subbie's particular strategy, this is the distance that we need to figure out.

What is the distance between 601 and 256.

Looking at our 601, this is actually going to cause for a re-group and Minnie and Subbie do not like to re-group.

So we're gonna shift that number line, we're gonna actually go back two, and we're going to shift it to 599, because Minnie and Subbie, like working with the nines.

Let's take a look at what that actually means for the distance on our number line.

If we have here, we can see our original distance.

Our tail is nice and tight, but by Minnie going back two.

It actually has made their tail very droopy.

And if we remember the girls do not like their tail dragging in the mud.

So by going back two, that has caused it to droop and we need that tail to go nice and straight.

So now we have to move the subtrahend back two.

So am gonna go ahead and back up my number line to now be 254, to see if that makes our tail straight.

So now let's take a look at our new distance, going from 254 to 599, but now we also need to check it with our string and make sure that tail is nice and straight.

So if I align up at 599 to 254, it's nice and straight, just like it was.

Now that the number line has shifted it's time to subtract.

Setting up our new equation we now have 599 minus 254.

It's much easier now to subtract nine, take away four is five 90, take away 50 is 40.

And then looking at five hundreds, take away two hundreds.

I have 345, which makes my answer 345.

601 take away 256 equals 345.

Nice work with that strategy, boys and girls.

I wonder if you can show someone how you use compensation and shift that number line so that you don't have to re-group just like Minnie and Subbie.

You remember our good friend DC, it looks like he has a subtraction problem for us to solve today.

He wants us to decompose or compose 262 take away 135.

Let's see how DC would do this.

So looking at 262 takeaway 135, DC would decompose this number 200, 60 and two.

And then for our 135, DC would decompose 100.

He would take out those 30 and the five.

And now he would like to subtract those, to see if there's anything that needs to be re-named.

So looking at my hundreds, I can easily take 100 from 200 to get 100, looking at my tens, I can take 30 from 60, and then I get 30.

However, looking at my ones.

Now this is where we have the problem.

You can't take five from two, because that's a negative number and we are not there yet.

So DC is going to have to do something a little bit different with this particular problem.

So DC realizes that we are gonna need more in our ones column in order to subtract five.

So he's gonna take that mallet and he's going to decompose his tens to give us some ones.

So now we still have two hundreds, but instead of six tens, we're actually going to stay with five tens.

And then we're going to take that ten and rename it so that we have 12 ones.

Now think about that though, 200, 50 plus 12.

Is that still going to give me 262?

Well, 200, 50 and then yes, 262.

We still have 262, even though we've just decomposed it a different way.

Looking at our second number, we have 135 and that number is okay.

So DC is gonna go ahead and leave that.

We have 100, we have three tens and five, and now we're gonna see if this is a more friendlier numbers to subtract from.

Now subtracting, we are gonna start with our ones.

So I know I can now take five from 12 and I get seven.

If I have 30 tens, I can take that away from 50 tens and I have 20 and next looking at my hundreds, 200 takeaway 100, I have 100.

If I add all of those up, I have a 127.

So now I know that 262 minus 135 equals 127.

Excellent work with that third graders with using DC's strategy.

But as we were solving that, you know what I was thinking of.

I was thinking of our senior citizen at Mathville T-Pops.

(upbeat music) Let's see how T-pops would solve this.

So T-Pops using his traditional method, would write out the problem.

262 minus 135, but looking at DC's strategy too.

I'm wondering how those two strategies compare.

So if T-Pops has 262, and I know that we need to rename this.

It actually would rename those 60 into our five tens, which would actually give us our 12 ones, which gets us the 200 plus 50 plus 12.

Now using T-Pops' strategy.

Now that we have renamed those, we can easily subtract just like we did with DC.

So if I have my 12 ones take away five, I have seven ones.

If I have 50, take away 30, I now have two tens or 20.

And then my 200 minus 100, I'm left with 100, just like we saw down here with DC, 100 plus 20 plus seven.

Our answer is 127, great job third graders and great job using all of those strategies today.

We started off with Springling and using and counting up and down on an open number line.

Then we had our Minnie and Subbie and we were using compensation by shifting the number line.

We then went to our friend DC who likes to decompose and compose those numbers.

And then we ended with T-Pops, who showed us how to use that traditional method.

Thinking about all those strategies that we used today.

Do you have a favorite?

Do you think there's a strategy that you could explain to someone when dealing with subtraction?

Now it's your turn to solve subtraction problems with the Math Mights, just like we did on today's show.

Excellent work, third graders.

What a show?

We started off with our Mystery Math Mistake, helping Springling out.

And then we learned how to subtract within a thousand using so many of our strategies.

And so many of our Math Might characters came to visit today too.

I can't wait for next time, but until then, bye.

(upbeat music) - [Narrator] Sis4teachers.org.

Changing the way you think about math.

- [Woman] The Michigan Learning Channel is made possible with funding from the Michigan Department of Education, the state of Michigan, and by viewers like you.

(upbeat music)