(gentle music) (bright sound) - Welcome, second grade Math Mights.

I'm so excited that you've joined us today.

My name is Mrs. McCartney.

Today we're gonna be having some fun with math together.

Let's check out our plan for today.

To start off, we're gonna do a number talk together and then we're going to compare, add, or subtract.

Let's start off first with warming up our math brain with a number talk.

Do you remember doing a number talk before?

The first step is we're gonna pose a problem.

I'm gonna choose an operation with something you're already familiar with and then we're gonna try to solve it mentally without pencil and paper.

Last, we're gonna share out our strategies together to see how you solved it.

Let's see which Math Might is gonna help us solve our first number talk problem so we can get warmed up.

Let's see who it is.

Have you met our friend Abracus from Mathville?

He's one of the most magical Math Mights that we have.

He wears a top hat and carries a wand.

He loves to play magic tricks on numbers.

He uses a strategy that's called compensation.

Compensation is raising to take his wand and zap a number temporarily, hold onto the change that he made in his wand, and then zap it back.

Let's see what Abracus' problem is for us today and I want you to be thinking about is there a number that you could zap to make it easier to add mentally in your head?

Let's see what he has.

Abacus wants us to solve the problem 25 plus 26.

Remember, you're not using pencil and paper to solve this, we're just thinking about that problem mentally.

Does 25 plus 26 remind you of an easier fact that you might know?

We oftentimes call Abracus' strategies doubles plus one or doubles minus one, you may have heard it as doubles plus two or doubles minus two.

It's using the strategy of compensation.

Let's see how our friends solve this problem.

Rocco says I think the answer is 51.

I know that 25 plus 25 is 50, but if I add one more, it is 51.

Did you think of this strategy like Rocco did?

Let's model Rocco's strategy to make sure we understand how he's using Abracus' strategy.

Here we have the problem 25 plus 26.

Rocco said he added 25 plus 25.

I wonder where he's getting that from, 25 plus 25, I see 25 plus 26.

Let's build it on the abacus to see exactly how he's looking at it.

We have our first add in, which is 25, our second add in is 26.

Do you see where he could have made this 25 plus 25?

If I move this one off to the side, it is 25 plus 25.

Abracus likes to zap a number to make the addition problem simpler.

Let's make a note of that over here.

He took the number 26 and subtracted one.

Imagine this being held in Abracus' wand and then he decided to add an easier problem 25 plus 25.

That's an easy thing to add.

What does that make you think of?

Let's see what Aidan says.

Aidan says he thought of it the same way and it reminded him of counting quarters, 25 plus 25 equals 50.

So we're gonna put the 50 here, but we know we have to zap it back so Abracus will want to zap back that one that he put in his wand and make it one more.

That's where Rocco thought of 50 plus the one from the one he took away to get 51.

Great job, Aidan and Rocco on our number talk using Abracus' strategy.

Did you think of that strategy to use?

I wonder if you have other problems that are similar to those that you could use Abracus' strategy with.

Let's check out our I can statement for today.

The I can statement is I can compare numbers and add or subtract.

Let's see our first problem.

Tyler and Elena were asked to find the value of 81 minus 79.

On the left side, you'll see Tyler's way.

On the right side, we'll see Elena's way.

What do you wonder and what do you notice about the two different strategies that were used?

They definitely used something different.

Let's see what Rocco and Aidan think.

Rocco notices that it looks like they both got the same answer, which is true.

Aidan says he notices that Elena used Springling's strategy and Tyler used T-Pops strategy.

Did you have those same notices that the boys did?

Let's see what their wonders were.

Rocco wonders is T-Pops the most efficient strategy to use with this problem.

And our friend Aidan says, is there another way that we can solve this problem?

Those are both really great wonders.

Do you think using T-Pops strategy is more efficient or using Springling's strategy with this particular problem would be more efficient.

Let's check out both strategies so we can really compare and decide which way that we should subtract.

Let's check out Tyler's strategy first with our friend T-Pops.

T-Pops is the oldest citizen in Mathville.

He wears glasses, has gray hair and even has a cane when he walks around.

He loves the traditional method like your mom and dad and I learned when we were in school, but he also wants students to learn the three ways plus the traditional with the other Math Might characters.

Let's first check out how Tyler solved using T-Pops strategy.

We have 81 minus 79.

81 is our minuend which we have built in the disks on T-Pops place value map.

The subtrahend is the second number which we have built with the strips.

Let's separate by place value to see what we should do first.

One minus nine, I'm gonna take the nine and see if I can try to pick up nine from the one.

We do not have enough.

So in this case, we know that we have to figure out how to rename the number 81 because we can't take nine away from one.

We can go over in the tens column and rename the number.

I'm gonna go ahead and put 10 ones in the one column to make this so that we can subtract it.

We now have renamed 81 into 70 and 11.

In this column over here, we're gonna go ahead and show the renaming that we made.

We took the number 81 and we made it seven tens and 11 ones.

Does seven tens and 11 ones still equal 81?

Let's double check.

If we have 70, we add this 10 and we have 80, and now we have one.

Do we go next door and borrow and say we're gonna give it back?

If I borrowed your jacket today, you would want it back, wouldn't you?

So we didn't necessarily borrowed, we just renamed or regrouped our eight tens and one ones into seven tens and 11 ones.

Now we can subtract a whole lot easier.

I'm gonna take my nine.

I had one, I want to pull off nine out of my 11, one, two, three, four, five, six, seven, eight, nine and I'm going to take it away.

11 ones minus nine ones is two ones.

This might be kind of easy because we have 70 minus 70 or seven tens minus seven tens.

When I take this away, I'll know that I have nothing left in my tens column so the answer is two, 81 minus 79 is two.

Wow, that was a lot of work to use T-Pops strategy.

We had to build the minuend and build the subtrahend and do some regrouping and renaming just to get the answer two.

Now that we see the way Tyler solved it with T-Pops, let's check out the way Elena solved it with our friend Springling.

Do you remember our friend Springling from Math Mights?

She was born with fancy eyelashes and fluffy fur and a large coily tail.

She secretly loves to do addition while she's doing subtraction and loves to hop on an open number line.

Let's compare and check out Springling's strategy in comparison to T-Pops to see which one might be more efficient.

Here, we have 81 minus 79.

Springling just wants to find the distance between these two numbers.

She really enjoys hopping on friendly numbers so she was on the number line at 79, what would be the next decade number that would come up?

So you were thinking of 79, 80 is really close.

So let's go ahead and plot 80 on our number line and say hop, Springling, hop.

Springling just went one on the number line to 80.

She only needs to go from 80 to 81.

That's easy, hop, Springling, hop, that's one.

She likes to count the hop so one plus one is two.

Hey, that gives us the difference from 81 minus 79.

Now, my question for you is which strategy was more efficient to use T-Pops with the traditional method or do you think using Springling was a little bit easier?

You can see two of our vehicles in Mathville.

Down below was our car that kind of passes along Mathville and drives slowly as they're going from place to place.

Then we have the super fast jet plane that flies through Mathville and wants to get to strategies really fast.

So let's think about do you think that T-Pops strategy was the jet plane with this problem, 81 minus 79 or do you think it was the car that was kind of poking along to get to the strategy?

Do you think Springling's strategy was the car method or the jet plane?

Let's see what our friends Rocco and Aidan have to say about this.

Rocco said Springling's strategy was way easier because you only had to hop two.

Aidan says I think T-Pops strategy with this problem was a car method.

I have to say that I agree.

Sometimes in math when you start to add or subtract, you really should compare the two numbers that you're adding or subtracting to see which strategy is more efficient.

Let's check out this next problem.

It says can you solve 203 minus 198?

I saw Springling on there hopping, kind of leaning us towards her strategy.

Do you think that Springling's strategy for this particular problem would be easier or do you think using T-Pops?

Let's check it out.

Let's go ahead and put T-Pops strategy on here just so we can kind of think about this before we decide which strategy is the most efficient.

203 minus 198 would be starting in the ones column.

I can't take eight away from three.

This is gonna involve a lot of regrouping.

I don't know if T-Pops strategy is the most efficient.

Let's try looking at Springling.

Springling wants to look at the distance between the two numbers, between 198 and 203.

Well, if we were counting, that isn't that far to find the distance between the two numbers.

If I'm at 198, we know that we could hop up to 200, which would give us only two to hop, that would make it a little bit easier.

Do you think you could do 200 all the way to 203?

Hop, Springling, hop, that's only three.

Two plus three is five that shows us the distance between 198 and 203.

If we were gonna go over to T-Pops strategy, it certainly would not be solved that fast so which strategy do you think is the car method and which strategy is our jet plane?

Well, if we look here over at our Springling strategy, I'm gonna name that as the jet plane, we got there in a cinch.

If we were to go through the whole process of using T-Pops strategy, it would take us a whole lot longer.

It's important, second grade, just to slow down for a second to look at the problem to decide which strategy is most efficient.

The jet plane doesn't mean that you're flying through the math faster, it's which strategy is going to be the most effective or easiest to get the answer and in this case, Springling's strategy definitely wins as the jet plane strategy.

Can you solve 680 minus 673?

Do you think Springling's strategy is the right way to do it or do you think that T-Pops will be more efficient or maybe another Math Might?

These are the types of questions that you get to ask yourself now while you're subtracting.

It's your turn to subtract with Springling and see if another way might be more efficient.

Thanks so much, second grade Math Mights.

We've had so much fun today back from our number talk with my friend Abracus, the most magical character in Mathville to working on looking at comparing first and then deciding which strategy you should use in subtraction.

I know that you're gonna do a great job thinking if you're using the car method or the jet plane.

I sure hope that you join us for another Math Might episode soon.

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- [Girl] Changing the way you think about math.

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