# Lesson video

In progress...

Hi, everybody.

Today we are going to be putting our investigating hats on, because we're going to be trying to work out all these different numbers that could've been rounded to a nearest multiple of 10.

So before we hit begin, let's put on our hats, tighten those ties, and tell the computer, now I'm a mathematician.

Super job.

Let's get started.

So here is our lesson agenda for today.

We're going to begin with our Star Words, then we're going to be rounding to the nearest 10, we'll do some investigating to which numbers could've been rounded, and then you're going to go off and do your own task in Mystery Numbers.

But before we begin, please make sure you have a pencil, a piece of paper, and a ruler.

If you need to go get anything, please pause this video now and make sure you have everything.

If not, let's get started.

So here are our Star Words.

Rounding.

Nearest multiple.

So you only have two today: rounding and nearest multiple.

Let's make sure we use them lots today.

So here we have the number 29, and we need to round it to the nearest 10.

So our nearest 10 would be 30.

What other numbers could be rounded to 30? 28 could be rounded to 30.

27 could be rounded to 30.

26 could be rounded to 30.

25 could be rounded to 30.

Could 24 be rounded to 30? No.

You're very right, it can't, because remember, one to four, we hit the floor.

So we round down.

And five to nine, we reach up high.

So we'd round up.

So 25 and up we round to 30.

So are those the only numbers that will get rounded to 30? What about these one to four? Well, 31 could be rounded down to 30.

32 could be rounded down to 30.

33 could be rounded down to 30.

And 34 could be rounded down to 30.

Could 35? No, you're very right.

35 would have to be rounded up because five to nine, we reach up high, and we'd have to round it up.

What about 70? What numbers could, what numbers could be rounded to 70? So here we have our number line and we've got 70 on there.

So the first number that could be rounded up, rounded up, thank you so much for reminding me, is 69.

68 could also be rounded up to 70.

67 could be rounded up to 70.

66 could be rounded up to 70.

65 could be rounded up to 70.

64, oh, no? Okay, 64 can't, because 64 we have to hit the floor.

Well done.

And 64 would be rounded down to 60.

Are those the only ones that could be rounded to 70? No, well done.

I tried to trick you there.

71 could be rounded to 70, so we round down.

72 could be rounded down to 70.

73 could be rounded down to 70.

And 74 can be rounded down to 70.

Well done, everybody.

Which numbers could've been rounded in these multiples? For example, which numbers could be rounded to 30? Which could be rounded to 50? Which could be rounded to 70? Which could be rounded to 40? Which could be rounded to 60? And which could be rounded to 80? So pause this video, draw your number line, and write which numbers could've been rounded.

Great job.

So these are the numbers that could be rounded.

So the numbers rounded to 30 are 25, 26, 27, 28, 29.

They could all be rounded up to 30.

31, 32, 33, 34 can be rounded down to 30.

45, 46, 47, 48, 49 could be rounded up to 50.

And 51, 52, 53, 54 could be rounded down to 50.

65, 66, 67, 68, 69 can be rounded up to 70.

And 71, 72, 73, 74 are going to be rounded down to 70.

35, 36, 37, 38, 39 can be rounded up to 40.

And 41, 42, 43, 44 can be rounded down to 40.

55, 56, 57, 58, 59 can be rounded up to 60.

And 61, 62, 63, 64 can be rounded down to 60.

And last, but not least, 75, 76, 77, 78, 79 can be rounded up to 80.

And 81, 82, 83, 84 can be rounded down.

So remember, we have our sum that will help us.

One to four, we hit the floor.

Five to nine, we reach up high.

So we round up if it ends in a five or a nine.

So here we have mystery numbers.

Now this is one of my favourite things to do.

So we have the number 170.

Clue one, the number can be rounded to 170, so it could be all the numbers, 165, all the way up to 174.

Clue one.

Clue two, it's an odd number, so I need to cancel out all of the even numbers.

So I'm going to cross out 166, 168, 170, 172, and 174.

It's a multiple of five.

So it needs to end in a five or a zero.

So I can cross out 167, 169, 171, and 173.

So the answer left is 165.

So it's going to be your turn now.

So you have four questions with some clues in.

So what you need to do is to draw your number lines, read the question carefully, and find the mystery number.

So pause the video and I'll see you soon.

Well done, everyone.

I hope you enjoyed doing that as much as I did.

Let's go through these together.

Question one, this number has been rounded to 140.

So these are all the numbers that could be rounded to 140.

It's an odd number, but the tens digit is even.

So we are doing lots of crossing out now.

If you add the digits, the total is six.

So I know 143, one, four, add three.

And it's too much, so the mystery number is 141.

Question two, this number's been rounded to 220.

It's a multiple of five.

So here are all of our numbers that are rounded to 20, and here are all the ones that are not multiples of five.

It's an odd number.

Well, 220 is even, which leaves 215, therefore the mystery number is 215.

This number's been rounded to 170.

It is not a multiple of five.

And this number is the same, forwards or backwards.

So that means to cross out lots of these numbers, and the mystery number is 171.

This number's been rounded to 480.

480.

It contains one odd digit, but it's an even number.

The ones digit is greater than the tens digit, therefore the mystery number is 478.

Well done, everybody.

Give yourself a big one, two, three, well done, me.