(cheerful music) - [Children] Math Mights.

- Welcome second grade Math Mights.

My name is Mrs McCartney.

Thanks so much for joining us today.

I'm so excited to learn math with you today.

Today, we're gonna do a mystery math mistake and then we're going to start to work on making a dollar.

Let's start off with warming up our brain with our friends from the Math Mights as we do a mystery mistake.

No, all the Math Mights have all gotten turned around and messed up with their strategies.

It's your job with our mystery math mistake to help them to figure out how to correct their strategy.

You're gonna be in charge by using a magnifying glass to look closely at how we're solving this next problem.

See if you can figure out where the error is and see if you can explain it to someone.

Our friend T-Pops tried solving this problem but as you can see, he's all upside down.

Let's check out how T-Pops solved this problem together first.

Here we have 62 minus 36.

We built the 60 and the two as our minuend which is the first number.

Down below we have our subtrahend, which is 36.

We're gonna separate these into the tens columns and the one.

Two minus six, we know is four.

If we do 60 minus 30, we know that we're left with three or 3 tens.

So 62 minus 36 is 34.

Was there a mystery math mistake or did we solve that problem just like we should have?

Let's check out to see what our friends think Landon and Myles.

Landon said, when I added 34 plus 36, it doesn't equal 62 something isn't right here.

He is looking at the subtraction problem and knowing he can check it by doing the addition.

He can take the difference and add it to the 36 and it should total 62.

Let's try that out over here.

34 plus 36.

I know 30 and 30 equals 60 and four and six equals 10.

Landon has a good thought here.

That total 70, not 62.

So he's correct.

Something is not right with this problem.

Let's see what Myles has to say.

Myles says, when you're doing subtraction, you can't take 6 ones from 2 ones, so you forgot to regroup.

The answer should be 26.

He's saying over here, you can't take 6 ones away from two.

Here I have six.

Can I go and take away 6 ones when I only have two?

You can't do that.

That is correct.

What we need to do is to be able to regroup.

We have this 60, we need to change it.

Change our 62 into 5 tens and 12 ones.

As we do that, we're gonna take the discs to model what that should look like.

So I have my 6 tens, I wanna show it to have 5 tens.

So I'm gonna take this 10 away and I'm going to put 10 ones in the same spot on the board as it is in the ones.

When we look at this, do you think the value is still the same?

Do we still have 62?

Let's check.

50, 60, 61, 62.

We just regrouped or renamed it into 5 tens and 12 ones which is what you see here.

So now we can take six away.

We had two, three, four, five, six.

When we take that away, we know that our answer now is 6 ones are left.

When we go into the tens column, we have 50 and we have to take away 30, 10, 20, 30.

When we take that away, we're left with 20.

So 62 minus 36 is 26.

Have you ever done that as a second grader where you look sometimes in that one column and you just wanna do it quickly and you end up subtracting from the bottom up?

You have to remember the regrouping strategy that T-Pops taught us to rename numbers that we can subtract.

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

I can find combinations to make 100 cents.

Take a look at these four sets of money.

What do you notice?

What do you wonder?

Why don't I take a look at all of those different sets of coins, I also see something new, a dollar bill.

Let's see what our friends Myles and Landon think.

They said, I notice it takes twice as many nickels to have the same value as the dimes.

Let's take a look here.

He's talking here about the nickels and the dimes.

Let's count the nickels.

Five, 10, 15, 20, 25, 30, 35, 40, 45 50.

We know that this equals 50 cents.

When we look at the dimes, 10, 20, 30, 40, 50.

Landon is correct.

When we look at this, it's twice as many nickels to make the dime.

We could maybe even put our fingers over two nickels and skip count by tens.

10, 20, 30, 40, 50.

Great thinking Landon.

Let's check out to see what our friend Myles says.

He says you can have $1 with coins or with a dollar bill.

Let's see what he's talking about.

In this box, I see coins.

I see 25, 50, 60, 70, 80, 90, a dollar.

I'm gonna go ahead and write a dollar here.

Over here, you see our $1 bill which looks similar to a paper dollar bill if you have seen one.

This also equals $1.

So what he's saying is that he notices that you can have the $1 total in coins or in one paper dollar.

Those were really great notices.

Let's see what the boys are wondering.

Landon says, if I had 100 cents, could I exchange it for a dollar bill?

Our friend Myles said, if I wanted to have the fewest number of coins for a certain value, would I use nickels or dimes?

Those were really great wonders that both Myles and Landon had.

We're going to be discovering their answers in our show today.

Let's take a look at these nickels.

How much is this coin collection?

Do you know the great strategy as to how you could count those coins?

I bet you do.

Let's see what our friend Myles thinks.

He says, I counted 20 nickels which equals $1.

If we were to look at these nickels, we could skip count by fives to figure that out.

Five, 10, 15, 20, 25, 30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, whew a dollar.

That took me a long time to skip count by fives.

Can you make a collection using only dimes that has the same value that we just counted?

I think that might be a little bit easier if we thought about that way.

How could you use what you know about nickels to help you figure out how many dimes are needed?

Let's see what our friend Landon thinks.

He says, for every two nickels, we would need a dime so we need 10 dimes.

Let's give it a try.

If we were to look at these nickels, we could think of two nickels equaling one dime.

So if we put these kind of in between, we know that equals 10 and we could fill in the rest of these, kind of in between thinking about them as dimes because two nickels totals a dime.

So we could count 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or $1.

I bet this strategy will be helpful when you have a large amount of coins with multiple dimes and nickels.

You could kind of pair the nickels together and think of them as dimes to help skip counting or creating the value of the set of coins faster.

Let's take a look at these four coins.

What is the value of these four coins?

Let's see what our friend Myles says.

He says, I know four quarters equals a dollar.

Let's take a look at these 4 quarters.

We have 25, 50, 75, 100 or a dollar.

This same dollar that we have is equal to 4 quarters.

I wonder how many pennies would you need to have the same value?

While if we have our dollar, we know that that is worth 100 cents.

So if we wanted to create that in Penny's, my goodness, we would need 100 pennies to create $1.

That might take a long time to count.

Remember the poster that we created to keep track of the coins and different money that we're learning?

We can now add the dollar.

We have our pennies, nickels, dimes, quarters.

We now can put the dollar and we know that that it's equal to 100 cents, or like we just talked about, it's equal to $1.

Second grade Math Mights, you're doing a great job with counting 100 cents.

I wanna challenge you to see if you can go over 100.

If I had a dollar and a quarter, how much money would I have?

Do you think you can figure that out based on what we've talked about so far with money?

Let's see what our friend Landon thinks.

He said, you would have $1 and 25 cents, which could be written 1.25.

Here I have my $1 and 25 cents.

So I'm going to put the dollar sign and put one.

This is where we're gonna say that word and.

$1 and, how do we have over here?

25 cents.

You're doing a great job being able to count over 100 cents.

Let's see collection of coins and see how we do.

Andre emptied his pocket and found these coins.

What is the value of his coins?

I have his coins here on the board.

Now they're kind of not very organized to help me count.

So I think I'm gonna pull down all of the dimes first to help me skip count.

This time I'm not gonna write the values under it because I'm pretty good at skip counting by tens.

10, 20, 30, 40, 50.

We can't forget about this guy, 60.

Now we're gonna bring our nickels in because it's easy to know when we should switch from counting by tens and then start counting by fives.

This is a long row of coins.

So here we had 60.

Stop your brain from skip counting by tens and start skip counting by fives.

So 60, 65, 70, 75, 80, 85, 90, 95, 100, 105.

Stop your brain.

Now I want you to start counting by ones.

I'm gonna take my pennies and arrange them down here.

I find arranging my coins in this line especially from greatest to least really helps me to slow down.

Over here we were at 105, we're gonna continue counting up now by ones.

106, 107, 108, 109, 110.

If I wrote the number 110, I know that we have 110 cents.

How could I write it using that decimal point and the dollar sign?

Let's try this.

We're gonna put our dollar sign here, our $1 and 10 cents.

We don't need to put the cents sign here because we use the dollar sign and we can see that we have 10 cents here based on how we wrote $1 and 10 cents.

Great job second grade Math Mights counting all those coins that were greater than 100 cents.

Let's try another task.

Priya had $1 and 18 cents in her pocket.

Can you represent this in coins?

I wrote down the $1 and 18 cents.

If I only wanted to use coins, I bet there's a lot of different ways that we could create.

The one that comes to mind first is creating a dollar with 4 quarters.

I know that 4 quarters equals $1.

And if I wanted to make this simple, I think I could do a dime, which is 10.

A nickel makes it 15, 16, 17, 18.

Great job using that decimal point and the dollar sign to be able to create quantities of money that are larger than $1.

Now it's your turn to play handful of coins, where you're going to be able to count the values of coins higher than a dollar.

Second grade Math Mights, thanks so much for hanging out with me today.

I think we've learned so much about counting coins that are higher than a dollar.

I hope to see you next time.

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

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

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