(playful music) - Welcome back third graders.

My name is Mrs. Ignagni and I'm here for another exciting episode of Math Mights.

Let's go ahead and check out our plan for today.

First off, we're gonna warm up our brain with a mystery math mistake.

Then we're gonna do a whole lot of learning about rounding, but first let's start with that mystery math mistake.

Oh no, boys and girls, what's happened to our math characters.

It looks like their strategies are all mixed up.

What is going on?

Well, here's how it works.

What's gonna happen is that one of our favorite Mathville characters is going to share with us a problem that they're having a difficult time solving.

We are gonna be like little detectives and look closely at that problem and see if we can help out so that way we can come to the correct answer.

Let's see which one of our Mathville friends needs help today.

Look boys and girls, it's a Springling.

Springling needs our help solving 491 minus 288.

We're gonna go ahead and see how Springling solve this problem.

I'm gonna set up our open number line.

We have 491 minus 288, and I know that Springling loves solving on that number line.

Springling told me that she put 288 towards the beginning of her number line because Springling knows that 288 is a smaller number than that 491.

From there, she went ahead, put 491, and then her first big hop, she actually hopped all the way over to 488 because you know Springling, she loves to hop as far as she can.

So she went from 288 all the way to 488 covering a distance of 200.

And then from there, she was able to hop a distance of four to get to 491.

Now that we found her distance, we need to add it.

So if we have 200 plus four, that means that our total is 204.

What do you think boys and girls, did you see a mystery math mistake that Springling made?

Let's see what our friends say.

Fariah said I don't think Springling has the correct answer.

I know because when I add 288 plus 204, it equals 492 so it can't be correct.

I think Fariah is actually using the inverse operation to check this problem and to see if it's accurate.

So with the inverse operation, Fariah's saying that if we take these two numbers and add them together, we should actually get this number if our math is correct.

So if we go ahead and set that up and we have 288 plus 204, now that we've set up our equation, we need to add those two numbers together to see if it does equal that third number.

So if I have eight plus four, which is 12, I have my two ones and then my one 10 to show 12, then eight plus one is nine or nine tens and then two hundreds plus two hundreds equals four hundreds for a total of 492.

It looks like Fariah is correct, something is wrong.

Let's see what Dawson says.

Dawson said I think when Springling counted up from 488 to 491, she miscounted.

It should have been three, not four so the answer would be 203.

So if I'm understanding Dawson correctly, 488 to hop to 491 is actually three, not four.

So then if I added these together, my distance of 200 plus three is 203 so Dawson's correct.

491 minus 288 is 203.

What do you think boys and girls?

Is that the answer you got?

I know Springling would be so proud of us for figuring out her mystery math mistake and using her strategy all at the same time.

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

Our I can statement of the day is I can learn about rounding.

Today, boys and girls, we're gonna be talking about rounding.

Have you talked about rounding before?

Do you remember some of the key things we have to remember when we're rounding?

Let's see if our friends can give us some hints.

You'll see I have some chart paper with rounding at the top.

Some of our friends are gonna give us some ideas on how we can round and give us some little tips about it.

Our first friend says that you can round to the nearest 10 or a hundred.

Another one of our friends said that a number line and abacus can help you round numbers.

And lastly, our third friend said that you can replace a number by another number of approximately the same value.

What do you think boys and girls, would you add anything else to that list?

Let's see how our friends actually round some numbers.

Taking a look here, we have two friends, Andre and Claire, that rounded some numbers for us.

But what do you notice about these numbers and how they rounded?

What do you wonder?

It's almost like they rounded in two different ways.

Fariah agrees with me.

She said Andre and Claire rounded differently.

Claire only rounded to zero and 100.

Taking a closer look at her notice, she's right.

Claire rounded from 100 and zero only, zero and 100.

Dawson said they both rounded 99 to 100.

Looking at Dawson's notice, I see that here's 99 and you're right.

Both Andre and Claire rounded to 100.

So those are really great notices, but now let's check out what they're wondering.

Fariah wonders why do they have different answers whereas Dawson wonders why do they both have 100 when they rounded 99?

Those are really great wonders and that's actually what we're gonna be investigating today.

Let's use an abacus and a number line to help us understand their rounding.

So looking at Andre's first number 82 that he decided to round to 80, I'm gonna go ahead and show this on an abacus to show the reason why Andre chose 80 to around 82.

With my abacus, I know that it's cleared when I have all of my beads over here to my smiley face.

And remember, each row has 10 beads and they're separated by colors to represent five and five.

When I'm going to go ahead and record or remember what my abacus is showing, I know that I need to count them so I have 10 and two so I know that that's actually showing 12.

Moving that back though, if I wanted to represent 82, I'm gonna go ahead and do 10, 20, 30, 40, 50, 60, 70, 80, and then two, I now have 82.

Now Andre had to make a decision when he was rounding by tens if he in fact wanted to round to 80 or round to 90.

Now looking at our abacus, does it make more sense to round and move these guys over here to get to 80 or would it make more sense to push all of these over to get to 90?

Did you say 80?

That's exactly what Andre did.

He actually moved those over and so that is why he rounded 82 to 80.

Let's take a look at the next number 17.

I'm gonna go ahead and clear my abacus and I'm gonna represent my 17 so I have 10, 15, 17.

Now again, Andre has to decide if he's gonna round to 10 or if he's gonna round 17 to 20.

So does it make sense to move all of these over to get to our 10 or does it make more sense that we would actually be moving these three over to get to 20?

Well, Andre said that it made more sense to take 17 and round it to 20.

For our next one, we're gonna go ahead and show 63, which Andre rounded to 60.

So if I show my 63, 10, 20, 30, 40, 50, 63, again, thinking about whether I want to round to 60 or 70, looking at our abacus, it actually makes more sense to quickly move those guys over to get to 60 as opposed to again having those 63 and then moving seven over to get to 70.

So we're gonna go ahead and put those back and we're gonna move it over and that's how Andre found his 60.

So looking at Andre's last one, I'm gonna go ahead and represent 99.

Since I know there's a hundred, I'm just gonna quickly move that over and move back one.

So I have 99 on my abacus and now again, thinking about does it make more sense to round 99 to 90, or does it make more sense to round 99 to a hundred?

Should I move all of these over to make it 90 or I just have to move one to make it a hundred, just like Andre did.

Excellent work rounding to the tens Andre.

I can see very clearly now exactly why you chose the way you did.

Let's take a close look at what Claire did though.

So Fariah noticed that Claire was rounding to the nearest hundred.

She only used zero and a hundred.

Setting up our number line, I went ahead and labeled it zero to a hundred, but when we're rounding on a number line in the hundreds spot, I like to put in my mid point so that I can accurately gauge if I want around zero or if I want to round to 100.

So I'm gonna draw in my mid point here, which would be 50 and looking at our first number of 82, I'm gonna go ahead and plot that on my number line.

82 is gonna fall over here and I can see that 82 is actually closer to a hundred than zero, it's past that midpoint.

So now I understand while Claire decided to round 82 to 100 because that is the closest hundred that 82 is to.

Our second number is 17.

Now I know that 17 is gonna fall over here below our 50 midpoint.

So 17 is going to round to zero, which is exactly what Claire decided to do.

17 closely rounds to zero when you're rounding to the nearest hundred.

For the next one, Claire decided that 63 would plop somewhere in this area again after our midpoint of 50, which is why she chose to round 63 to 100, because it's closer to 100 than it is to that zero.

For our next number 47, this one can be a little bit tricky, but again, if we plotted out, we see that 47 again is going to fall below the 50, putting us closer to that zero than to our hundred, which is why Claire rounded to zero.

So for the last one, if you remember Dawson said that Claire and Andre both rounded 99 to 100.

When we're looking at our number line, when we plot 99 here, we'll see that it does in fact land close to 100 and so that is why Claire did round 99 up to 100.

Looking again though with our tens, when we have our abacus showing our 99, again remember it made sense that we would move that over so even though we're rounding by tens in this case, it still would make more sense to round to 100.

Boys and girls, you are doing so well with this rounding, I feel like we should try this out in a game.

Let's play Four in a Row, Roll and Round.

To play this game, you just need your Roll and Round game mat, and your Roll and Round accountability sheet.

I'm gonna go ahead and roll three dice, and then you're going to put them in order so that you can find a number that you are going to round to the nearest 10.

Now you're gonna have to be strategic so you're gonna want to think about in some cases which number you want to make and manipulate those dice to do so, but I'll show you what I mean.

Just remember the goal is to get four in a row.

So rolling my dice, I'm gonna go ahead and arrange my number into 643.

On my accountability sheet, I'm gonna write 643 and now knowing what I know about rounding to the tens, I'm gonna go ahead and round that to 640.

Now I'm gonna take my marker and I'm gonna go ahead and place my marker on 640.

I've done my part, now it's time for my partner.

Same procedure, my partner is gonna go ahead and roll the dice.

Rolling the dice, they're gonna go ahead and roll 362.

So using their side of the accountability sheet, they're gonna write 362.

Again, thinking about rounding to that tens place, 362 becomes 360.

Recording 360 and they're gonna take their yellow marker and go ahead and mark their board 360.

Remember boys and girls, if you're having a difficult time rounding to that nearest 10, you can always use an abacus or a number line to help you just like we were doing earlier.

I'm up again so rounding and deciding, I'm gonna go ahead and 421.

So I'm gonna record my number 421.

Again, I have to decide, am I rounding to 420 or 430?

Makes more sense to do 420.

And I'm gonna go ahead and put my marker.

Unfortunately, this spot is not anywhere close to this one, but remember the goal is four in a row so I am on track to possibly getting four in a row if I can make that 530.

So now they are gonna go ahead and keep playing until they get four in a row either horizontally, diagonally or vertically.

Now it's your turn to play Four in a Row, Roll and Round, just like we did today.

Excellent work today, boys and girls, we had a fun filled show.

We started off today solving like little detectives for our mystery math mistake and then we spent some time reviewing and learning all about rounding.

I had so much fun with you today.

I can't wait for next time, but until then, I'll see you later.

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