(cheerful music) - [Children] Math Might!

- Welcome, second grade Math Mights.

My name is Mrs. McCartney.

I'm so excited that you joined us today to learn more about math.

Our plan for today is to start off doing a number talk together, and then, we're gonna work more on adding and subtracting, but this time, with 10s or 100s.

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

Number talks are so much fun.

You've done them before, right?

First, we're gonna pose a problem with an operation that you're familiar with.

We want you to try to solve it mentally without using pencil or paper.

For the last part, we're gonna share out how you solved and explain the strategy that you did.

Let's see which one of our Math Might friends is going to join us for our number talk today.

- Abracadabra!

- You remember our friend Abracus.

He's one of the most magical characters in Mathville.

He wears a top hat and carries a magic wand because he loves to zap numbers to make them more friendly when he adds.

The strategy that Abracus uses is called compensation.

You might also know it as doubles+1, doubles-1, doubles+2, or doubles-2.

All of these strategies change the problem temporarily to make them easier to solve.

Let's see if you can use Abracus' strategy on our problem that he has for us today.

The problem is 58+22.

Think about that without using any pencil and paper.

How would you solve that mentally, and be able to explain your thinking?

Let's check out to see how our friends, Rocco and Aidan solved.

Rocco said, "I think the answer is 80.

I added 2 to the 58 to make it 60.

Then, I added 60+22 to get 82.

Then, I took off 2, and I added to get 80."

Wow!

That is kind of complex, the way that Rocco is explaining that strategy.

Let's do that together so we can make sense of how Rocco is using Abracus' strategy of compensation to solve.

He said, first he's looking at that 58 and he knows it's really close to 60, so he wants to zap the number and change it to 60.

He zapped it by adding 2 to the number.

We wanna make a note.

Then, he added it to the 22.

Let's take a look at it on the abacus.

First, we're gonna build the first add in, which is 58.

Below it, we're gonna add the number 22 down below.

Rocco thought that it would be easier to be able to add 2 to make this a nice even 60, because he could add the 60 plus the 22 to quickly see that the answer is 82.

Now, with Abracus' wand, he keeps the change in his wand to remember.

We added 2, so we have to take off 2 to see what the answer is.

When we take our 82 and subtract the 2, we know that we have the answer 80 that you can see here on the abacus.

I don't know about you, but I think that Rocco did a great job using Abracus' strategy.

Is that the only way that you could use Abracus' strategy with compensation?

Did you think of it a different way?

Let's see how Aidan was thinking.

Aidan said, "I solved like Rocco.

However, I just added the 2 to the 58 to make it 60, and then I took 2 away from the 22 to make it 20.

So, the problem was simple.

60+20=80."

Hey, that's not a bad idea to check it out that way.

It's almost like he zapped it twice.

Let's check it out to see how he did it.

He saw that 58, and wanted to just go ahead and make it a 60, so, he added 2.

Remember, Abracus is gonna keep that change in his wand.

On this side, he wanted to make this number a 20, so he subtracted 2.

Let's look at that on the abacus to make sure we understand.

Our first add in is 58, so we're gonna put 58 on here first.

And then, we're gonna build the 22 below.

10, 20, and then 2.

What he did was he added 2 to the 58 to make it a 60, like you see here.

And at the same exact time, he zapped the 22 to take away the 2 to make it 20.

Look at that.

That makes it easy.

60+20=80.

That's another great way to solve using Abracus' strategy.

It's like a zap zap, and you can get that answer really quickly mentally using either Rocco or Aidan's strategy.

Do you think you could solve using Abracus' strategy?

I bet you can.

Let's check out our "I Can" statement for today.

Our "I can" statement says, "I can add and subtract 10s or 100s."

When you're adding with 10s and 100s, there's no one better for Mathville for us to use besides Value Pack.

(cheerful music) Hey, Value Pack, come on over and help us.

(makes grunting sound) You remember Value Pack.

When they're clicked together, they show the full value of the number.

But, the cool part about Value Pack is they can separate and click apart, and show their value right on their belly.

So, if we have the number 27, together it would show 27.

When they separate, it will show 20 and then the 7.

That's a great way to help us to add or subtract 10s or 100s to a number.

Let's check out the first problem that we're gonna add using Value Pack.

We wanna start with the number 297.

Then, we're gonna roll a number cube and add ____ hundreds.

We wanna complete the equation of 297+__=__.

Here, we have the number 297.

We're gonna roll the die and pretend that this value is going to add it to the 100s.

I'm gonna go ahead and roll.

I ended up with a two, so we want to add to this number, 200.

It's important to slow down when you're adding 100s or 10s to really think about the value that you're adding.

We know that this can click apart, and look at just those 100s.

We want to add on another 200.

200+200, we know, equals 400, so we can create the number 497 when we click it back together.

297+200 =497.

Excellent work, second grade Math Mights.

That made it easy, especially using our friend, Value Pack.

Let's check out our next problem.

We're gonna start at 432.

Roll a cube and add __ tens, and then, we're gonna complete the equation 432+ __= __.

Remember, when you're looking at the die this time, the value is going to be worth 10s.

Here, we have the number 432.

I'm gonna go ahead and roll the die, and I know that that is one 10.

Value Pack is perfect 'cause we can click it apart.

We know that we're adding to the 10s value, and we need one 10.

If I carefully look at 30+10, I know the sum is 40.

Then, we can take Value Pack and click 'em back together to show our value of 442.

So, 432 +10, we know, equals 442.

Great work on adding the 10s and the 100s into the numbers.

Do you think now we can switch gears and try to subtract 10s or even 100s?

Let's check out the next one.

It says, let's start with 982.

Roll a number cube and then subtract ___ tens.

Complete the equation 982-___=___.

Let's try to do that together.

I have the number 982.

This time, the die that we're using is going to represent 10s, but we're going to subtract instead of add.

I'm gonna go ahead and roll.

It wants us to take away three 10s or 30.

When you're subtracting with 10s and 100s, again, it's really important to slow down and look at the place of value that we're using, because Value Pack can help you if you look at the value of the numbers.

We know that the red is in the 10s, so, we're gonna click apart Value Pack here, and I know that I need to take away 30.

So, if I have 80 and I take away 30, I know that that will be 50.

When I put it together, we can put our 900, and our 50, and our 2 to get 952.

Now that we know how we subtracted, let's go ahead and put it in our equation.

982 minus our 30, we know, gives us 952.

You're getting really good at this.

Let's see now if we can subtract within the 100s.

Let's see the next problem.

Start with 805.

Roll the number cube and subtract ___ hundreds.

Then, we're gonna complete the equation 805-____=___.

Here, I have the number 805.

The die this time is going to represent the value in the 100s.

I'm gonna go ahead and roll, 200.

805 minus 200.

Just like Value Pack does, it's really important to look at the values of the number before we make a decision.

We know that we wanna take away 200 out of the 800.

So, I know 800 minus 200 is going to give us 600.

When I click this back together to show the value, we see that it's 605.

So, 805 minus 200 is 605.

Using place value strips does really help you when you're adding 100s.

Let's try now to see if we can use it with adding 10s.

Diego has six 10s.

Tyler has eight 100s, three 10s, and six ones.

Let's see if we can represent their values with place value discs, and find out what the value is all together.

We know that we started off knowing that our friend Diego had six 10s.

Next, our friend Tyler, we know had eight 100s, three 10s and six ones.

Let's add the 100s first.

Now, we have the eight 100s, we need to add on his three 10s.

And then, we know that he had six ones.

If we wrote the problem over here, we know we started off with six 10s, which was 60.

And then, we added eight 100s plus three 10s plus six ones.

If we put that together, we can look at our discs to see our value.

We still have our eight 100s.

We know that we have nine 10s, and then we still have the six ones.

Great job using those place value discs to help us to add 10s and 100s.

Another great way or tool to use is to use base 10 blocks.

Let's check this out.

Tyler has the blocks that you see on the top part of the screen, and Jada has her blocks in the bottom part of the screen.

Let's see if we can write an equation for the blocks.

Here, I have Tyler's blocks which we know equals one, 100, 200, 300.

So, I'm gonna go ahead and write the equation, 300.

We want to add it to what Jada has.

100, 200, 210, 211.

When we add this together, it makes it really easy because we can see all the 100s equal 500, and then we still have our 11.

So, 300+211=511.

Take a look at these blocks.

Do you think you could write an equation for the blocks that you see?

It looks like this looks a little different because there's diagonal slashes through some of the 10s.

Let's first find out how many we have.

100, 200, 300, 310, 320, 330, 340, 341.

That's the amount that we're starting with.

It looks like they took away three 10s.

We know that three 10s is equal to 30.

So, if we look at this problem, 341 minus 30, we wanna figure out how many are left.

100, 200, 300, 310, 311.

We know that the equation should read 341-30=311.

Wow!

We have used three different tools to add 10s and 100s.

We used the place value discs, we used Value Pack with the actual place value strips, and then we just used base 10 blocks.

I bet that you're becoming an expert with adding 10s and 100s.

Now it's your turn to add and subtract 10s and 100s using a spinner where you can take a number, and either add ___ tens or ____ hundreds.

Second grade Math Mights, I've had so much fun with you today doing our number talk with our magical friend, Abracus and then working so hard on making adding 10s and 100s a cinch.

I sure hope that you'll join us for another Math Mights episode soon.

(cheerful music) - [Narrator] sis4teachers.org.

Changing the way you think about math.

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