(whimsical music) (spring boings) (chair creeks) (window squeals) - [Children] Math Mights!

- Welcome.

Second grade Math Mights.

My name's Mrs. McCartney.

Thanks so much for joining us today for another episode about math.

Today, we're going to do our mystery math mistake and then after that, we're gonna talk more about coins doing coin combinations.

Let's start off first with warming up our math brain with our mystery math mistakes from our friends, the Math Mights.

(magical music) Oh no!

All of our math might friends have gotten all of their strategies confused!

I think that you'll be a big help today to see if you can find our mystery math mistake.

Here's how it works.

One of our friends, T-Pops, is going to join us and he is going to share how he solved his strategy.

But he's all confused, so it's your job to use your magnifying glass to look carefully at how I'm solving the way T-Pops told me to to see if you can find that mystery math mistake.

The problem we're trying to solve today is 64 plus 27.

You know T-Pops, he's the oldest math citizen and he loves to solve it the traditional way.

So let's look at his mat here.

On T-Pop's place value mat, we have 64 plus 27.

I built the first add in on the mat with our tens to show 60 and then four ones.

It's our job to add 27 more.

So I'm gonna go ahead and put the 10 and the 20 and then I'm going to add the seven.

We're gonna put in one, two, three, four, five, six, seven.

When I look at my ones column, I know four ones plus seven ones equals 11 ones.

So I'm gonna put the one for the 11 right here.

We have to be able to rename that number, so I'm going to take off our 10 ones and make it a 10, leaving the one here as you see.

If we were to add these up, 60 plus our 20, we know that we get 81.

So 64 plus 27 equals 81.

Did you find the mystery math mistake that T-Pops did?

Or do you think that T-Pop solved it the right way?

Let's see what our friends, Nora and Laila think.

Nora says, "I feel something isn't correct with this problem, but I'm not sure what it is."

Laila says, "When you're doing the traditional method, you must regroup if there are more than 10 ones.

You should add the 10 from the 11 so it would be six tens plus two tens plus one 10 which would give the answer of 91."

Let's check that out over here.

We said that there were four ones plus seven ones that would give us 11 ones.

She is correct.

We did not bring in that extra group of one 10.

This makes the number 11 one 10 with one 1.

Don't forget, we have to be able to regroup and put that one 10 from the 11 in the tens column.

We see that we have our six tens and then our two tens.

Here is the 10 that made our 11.

It goes here in the tens column and we now can see that we have the answer of 91.

Did you find that mystery math mistake like Laila did?

Sometimes we know things don't go quite right in math but being a math detective and finding and being able to explain your reasoning will really help you in your math.

Let's check out our "I can" statement for the day.

"I can learn about quarters and find the value of different sets of coins."

Let's take a look at the coins that we've learned so far.

What are the names and the values of the coins that we know?

we've talked about what pennies are and that they have a heads and a tails and it's worth one cent.

We've talked about what nickels are where it has a head and a tail and it's worth five cents.

And then we have the dimes where you see the head and the tail and 10 cents.

What is this coin?

There's a new coin in town and the coin is called a quarter.

A quarter is silver, it's a little bit larger than the nickel.

We're going to talk about the quarter today and its value.

The value of the quarter is 25 cents.

Let's see if we can complete the table so each row shows a value in cents and two different groups of coins that have that value.

I have a column that says coins, what is the value in cents?

And then we wanna find coins with the same value that we see here.

I'm gonna count first, like we've learned with counting the larger values first.

10, 20, 25.

The value is 25 cents.

Can you think of a coin that we can use that has the same value as the two dimes and the nickel?

That's right, it's our new coin that we're talking about, our quarter.

So I'm gonna place the quarter here.

In our second row, we have two quarters.

It's important as a second grader to learn how to count by 25.

So we have 25 and if we doubled 25, it would be 50.

So two quarters could equal 50 cents.

How can we show another coin or group of coins that would equal the value of 50 cents or two quarters?

I think we could use dimes to show that.

Let's try it.

10, 20, 30, 40, 50.

Five dimes equals the same as two quarters.

Let's move on to our next one, starting with the larger value, our dimes.

10, 20, 25, 30, 35, 40, 45, 50.

We can put the total here of 50 cents.

Hey, we found a third way to make 50 cents.

We also could show the value of that another way by putting the two quarters down.

We're gonna put in two quarters to show the value of two dimes and two, four, six nickels equaling the same as two quarters.

Down here, we're going to add up three quarters.

Remember we talked about skip counting by 25s?

25, 50 and then 75, three quarters equals 75 cents.

How could we show that with coins a different way?

We could use a combination of dimes and nickels, maybe?

Let's try that.

10, 20, 30, 40, 50, 60, 75.

Here we have seven dimes and a nickel to total 75, which is the same as three quarters.

Let's check out our last one here.

This is a little bit easy because it's only using nickels.

five, 10, 15, 20, 25, 30, 35, 40, 45.

Here we have 45 cents.

How can we create 45 cents using different coins?

That one was using all nickels.

I wonder if we could do a combination of quarters and dimes.

Let's see.

This is a little bit trickier.

We start off counting 25.

Then we have to skip count by tens.

25, 35, 45.

This will give us the same value as all of these nickels.

Another way that we could show 45.

That was fun counting coins different ways and finding different values that didn't have the same group of coins to equal that total value.

Let's see mow if we can count combinations with all the coins that we've been working with.

Take a look here, we see Elena's coins.

Elena has nickels, pennies, dimes and quarters.

What would you do to find the value of these coins?

If we're working with four coins, what strategy would you use to count the four types of coins?

Let's see what Nora and Laila think.

our friend Laila says, "I think you must organize the coins before you start counting them, so you don't miscount."

What do you think about Laila's idea?

When you have all those coins in front of you and they're all mixed up, that can be hard as a second grader to count them.

Let's take a look down here.

I went ahead and took all of the coins and I put them in order from the largest value to the smallest value.

So we can start here with 25 cents.

We know if we double 25 cents to show two quarters, that equals 50 cents.

Now we need to stop and skip count by tens.

So 50 cents, 60 cents, 70 cents.

Remember, we need to stop now.

We've been counting by tens and we have to switch to counting by five.

So 70 cents, 75 cents, 80 cents.

Now stop one more time and start counting by ones.

81 cents, 82 cents, 83 cents.

We see that there's 83 cents all together.

Let's take a look and see what Nora's idea was.

Nora said, "I would start with the quarters, then the dimes and then the pennies.

This way, it makes it easier to count up."

That sounds similar to how we just did it but let's check out how she's doing it, maybe with it not as organized.

I'm gonna use a strategy that a lot of second graders like to do to keep track.

We know we're gonna start with the quarters, then the dimes, then the nickels and then the pennies but we're gonna keep the count as we go.

If we start off here, we know that this is 25 cents.

If we continue here, we know 25 doubled is 50 cents.

Now we have to stop and think of skip counting by tens.

So if I had the 50, I would add the next one on to skip count by tens to get to 60 cents and then go to the next 10 cent, which is the dime to make it 70 cents.

Now we have to stop and think of how we're going to focus our attention on skip counting by fives now.

So 70, 75, 80, 81, 82, 83.

Which way did you prefer counting the coins?

Did you prefer counting them where we ordered them from largest to smallest and then we ended up counting them?

Or did you prefer it the way that our friend Nora did it, where she did it on the picture?

I don't know about you but if you have the physical coins while you're counting, it's a lot easier to start by putting them in order and then knowing when to stop skip counting by maybe tens and then switch to fives.

Let's try something more challenging.

Can you make 66 cents with the fewest coins possible?

I want you to think about 66 cents.

If you had coins in front of you, what would be the least amount of coins that you could use to make 66 cents?

Well, I know if I'm thinking of the number 66, do you think that there is at least two quarters in 66 cents?

We know that one quarter equals 25 and another quarter equals 50.

So if we were to label that 25 cents plus this quarter would make it 50 cents.

Could I pull an additional quarter down?

What do you think?

Well, no, we would be at 75, so I don't think that we can use any more quarters to show 66 cents.

Let's keep going to the dimes.

50, if I bring one dime down, I know that it's 60 cents.

Can I bring another dime down?

That would make us at 70 cents.

We know that that would be way too high, so let's put it back and go to our nickels.

If I add a nickel on, we know it's gonna add on five, so it would be 65 cents.

Could we add on another nickel?

That would again bring us to 70, too high.

We only need one more cent to get to our 66 cents.

So two quarters, a dime, a nickel and a penny are using the fewest number of coins to make 66 cents.

Now it's your turn to play coin compare level two.

It's similar to level one but this time we're gonna include the quarters, the dimes, the nickels and the pennies and you can compare it with your partner to see who has more.

Second grade Math Mights, I've had so much fun hanging out with you today.

From doing our mystery math mistake with T-Pops, helping him get his strategy correct and then we did so much with counting coins with now bringing in the quarter.

I'm so proud of all your work.

I hope to see you again soon.

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