(playful music) - Welcome, first grade Math Mights.

I'm Mrs. Markovich, and I'm so excited that you're here with me today.

I have so many great math activities that I know you're going to love.

Speaking of math activities, let's check out our plan for the day.

Today, we'll be solving a mystery math mistake, and we'll talk about subtraction strategies.

Let's warm up our math brain with a mystery math mistake.

Oh no, all of our Math Mights have gotten their strategies all mixed up.

What are we going to do?

DC is holding Abracus' wand.

So here's how our mystery math mistake is going to work.

One of our Math Might characters will be featuring a problem that they're struggling with.

It's your job to help them find the mistake and solve the problem correctly.

Let's see who needs our help today.

It looks like DC needs our help.

He has the problem six plus eight, and he's decomposed it into three and three.

Let's take a closer look at that on mine.

Here, we've got the problem six plus eight and DC decomposed the six into three and three.

Then he said, I know eight plus three equals 10 plus the other three equals 13.

Did you solve it the same way as DC?

Let's ask our friend Dawson.

Dawson says DC is incorrect.

He needed to decompose six into two and four.

Oh, okay, I think we better take a look at this on mine and solve it using the double 10 frame map.

He decomposed it into three and three.

So I'm going to take three from the top and put them on the bottom to make a ten, one, two...

Wait a minute.

He's right, I can't put three on the bottom to make a 10.

So I think what Dawson was saying was that it needed to be, if we change these two numbers, we needed to decompose the six into two and four.

So if I put the four here and the two here, now we know eight and two make 10 plus that four will give us the total of 14.

Wow, I'm glad that we had Dawson here to help us out.

This is great work.

Let's see what our I can statement of the day is.

It says I can subtract by counting up or taking away.

Today, we're going to be talking about different ways to subtract.

It looks like Diego and Tyler solved the same problem differently.

Did you know in first grade, we could solve subtraction problems differently?

Well, let's take a look at what Variah is thinking about how Diego solved his problem.

She said he puts 15 counters in the 10 frames.

Then he took away eight.

He counted what was left.

I think we need to take a closer look at what Variah's telling us about Diego strategy.

So here you can see that we have Diego's strategy where he has 15 counters in the double 10 frame.

Then he took away eight.

So if you had eight counters on your 10 frame, you would physically take them away.

On mine, I've drawn a line through them to cross them off to show 15 minus eight.

Then he counted what was left on the double 10 frame.

So on ours, we're going to count the ones that are not crossed off like this, five, six, seven.

And I know that you're really good at subitizing so you probably already knew that.

So we know that 15 minus eight equals seven.

Did you solve it the same way that Diego solved it or did you solve it a different way?

Let's take a look at how Tyler solved it.

Dawson's going to explain it to us.

Dawson says he put eight counters in the 10 frame, then counted on adding yellow counters until he got to 15.

He counted the yellow counters to get to his answer.

I think we need to talk about this a little further.

It sounds a little complicated.

So what Tyler did was put eight counters in the double 10 frame.

Then he counted on and stopped when he got to 15 and for each number, he put in a yellow counter.

So he said eight, nine, 10, 11, 12, 13, 14, 15.

Then the last thing he did was go back and count the yellow counters that he added.

So he had five, six, seven, the same thing that we got for Diego's answer.

Wow, that was a completely different way to solve the problem by counting on and we were able to solve the same problem in two different ways.

I'm really excited about the way that Tyler solved it, because I think we can call on one of my friends to help us.

Let's call on my friend Springling.

Springling is a Math Might that lives in Mathville and Springling has fluffy eyelashes and long hair and a tail that looks like a spring.

Springling likes to hop on the number line in friendly chunks.

And then when she's done hopping, she likes to keep track of how far she hopped so she can solve the problem.

Let's see if Springling can give us a hand.

Here's Springling ready to solve the problem 15 minus eight and it looks like she's going to be using a number line.

So what I've got here is the problem 15 minus eight.

We're going to start on this eight right here, and we're going to hop with Springling to the 10.

And I'm going to put the two...

I'm gonna put it inside of my bubble just because I'm running out of space.

Then from here, Springling is gonna hop all the way to that 15.

And you can see that there are one, two, three, four, five spaces in there so we're going to put a five right here.

Then I'm going to take the two numbers two and five and add them together to get the total of seven.

So I know that 15 minus eight equals seven, the same answer that both Diego and Tyler got.

Let's see if we can solve this problem 17 minus eight three ways, Diego's way, Tyler's way, and Springling's way.

Let's start out solving it Diego's way.

So if you can remember, Diego took 17 and filled in the double 10 frame.

We're going to take our marker and make 17.

One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17.

And then if you remember, Diego took away some so we are going to take away eight.

Since I can't physically take them away, we're going to draw a line through them.

And I'm going to do that with a different color marker.

Let's take away eight, we'll start here.

One, two, three, four, five, six, seven, eight.

The last thing that Diego did was count how many were left.

Let's do that now.

In fact, you're so good at it, I don't even think you need to count.

You can just subitize and see that there are nine left.

So we know that 17 minus eight equals.

Now, are you ready to try it Tyler's way?

Let's give it a shot.

This time we have the same problem 17 minus eight.

Remember, Tyler starts at eight and then counts up to 17.

Let's try it.

One, two, three, four, five, six, seven, eight.

I'm gonna switch my marker and count up to 17 then I'm going to go back and count my yellow circles.

So we have eight, nine, 10, 11, 12, 13, 14, 15, 16, and 17.

Now let's go back and count the yellow circles.

We have one, two, three, four, five, six, seven, eight, nine, the same answer that we got for Diego's.

We'll put a nine right here.

And last but not least, I'm gonna scoot my board up, invite my friend Springling over, and we are going to use a number line to solve the last one.

I'm going to write my numbers in up to 17.

One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, and 17.

Then Springling is going to start on the eight.

So I'm going to circle the eight and I'm going to use a different color just so you can see it better.

So I'm going to circle eight and Springling hops to a friendly number.

So Springling is going to hop to the 10 and we know that would be two.

Then Springling is gonna hop all the way to the 17 from the 10 and that gives us one, two, three, four, five, six, seven numbers.

The last thing I'm going to do is add two plus seven, which gives me the total of nine so I'm going to write nine right here.

Look at that, I got the same answer solving the problem three different ways.

First grade Math Mights, you're getting really good at this.

Let's try another one.

Let's see if we can solve 18 minus 15 three different ways.

We'll start with Diego's way.

We'll draw in the 18 circles.

Five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15, 16, 17, 18, then Diego is going to take away 15.

So we're going to cross off 15 of the circles.

One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15.

Now that leaves us with how many left?

We need to go back and count them.

One, two, three.

So 18 minus 15 equals three.

The next way that we're going to solve it is using Tyler's strategy.

Now Tyler counted on so let's do that now.

We're going to start with 15 counters, One, two, three, four, five, six, seven, eight, nine, 10, 11, 12, 13, 14, 15.

Then we're going to count on and stop when we get to 18.

So we say 15, 16, 17, 18, and then let's count how many we added on.

One, two, three.

We got the same answer as Diego, 18 minus 15 equals three.

We have one last way that we can try this.

Remember, that's with my friend Springling.

This time, we're going to start on the 15, which is right here and I'm going to circle that 15 and Springling is going to hop to the 18 just like this.

Wow, that was pretty quick.

You can see, I have one, two, three spaces there.

So now I know that 18 minus 15 equals three.

I was able to solve these problems with three different strategies.

Now it's your turn to try subtracting with take away and counting up.

I want you to remember to use some of the skills and strategies that you learned today.

Great work today, Math Mights.

I had so much fun with you.

We were able to solve a mystery math mistake with my friend DC and then we were able to do subtraction strategies with my friend Springling, where we were able to solve three different ways.

Until I see you next time, I want you to kiss your brain.

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