Let's see what you have learnt today about subtracting 3-digit numbers

Which of these 3-digit numbers has 2 in the hundreds column?

500 - 200 =

456 - 111 =

835 - 324 =

Which of these is the odd one out?

Subtracting Two 3-Digit Numbers (without regrouping) Quiz

﻿Hello everyone, I'm Ms Brinkworth. I'm going to be going through this math lesson with you today. What we're going to be doing is we're going to be learning to round numbers to the nearest 10. The reason for doing that is because we're going to be thinking about how to estimate for addition questions. So make sure you've got somewhere as quiet as possible and we'll get started. Hey, let's get started. Like I say what today's lesson is all about is working on our rounding skills so that we can estimate more accurately. Now, what we mean by estimating is a really good guess. It means that today's lesson isn't about finding the absolute correct answer but about doing it mentally and using what we know to have a really, really good guess at the answer. So here's our lesson agenda. What we're going to start with is recapping multiples of 10. So your 10 times table is going to really help you with today's lesson. We're going to practise rounding, and that's going to be rounding to the nearest 10. We're then going to use rounding to estimate. And then during your independent work and the exit quiz, you'll be estimating addition problems. So what you will need for today's lesson is just a pedal pencil, some paper, and a really good attitude. So please pause the video here if you need to go and get any of those things. And once you've done that have a go at these mental questions that means just doing them in your head please. Pause the video here and have a go at these questions. It shouldn't be too hard, but have a think about the strategies that you're using as you go through. Okay, how did you get on? Here are your answers but what I'm really interested in is whether you can see the strategies that you use to answer these questions. So for example, if you look at the first one, 40 add 30 is 70. I did that in knowing that 40 add 30 is a similar question to four add three. I know that four and three is seven so, 40 add 30, they're 10 times bigger. My answers will be 10 times bigger at 70. Again, if you look at that very last question 30 add 30, well, I know three and three is six, so I can make them 10 times bigger 30 add 30 is 60 Really well done. If you can do all of those questions really easily, it's going to help you a lot with today's lesson. So I'm all done If you had a go at the challenge as well. Adding multiples of 10 to get these amounts. Here are some ways you could have done it but there are lots and lots of different ways of getting those numbers. So well done If you were able to find some other ones. Okay, how would we then have a go at adding these larger multiples of 10? So for example, if we look at 150 add 20. Here's the answer of 170. But how do I know that's the answer? What fact did I use to get there? Well, I used the fact that five add two is seven. So, all I need to do is change the tens column in that question because the tens column is what I'm adding a multiple of 10. So I just need to add two to five to change that number from 150 to 170. And here are your other answers. And here are some other strategies I used. So for 300 add 70, I thought about 30 at seven is 37. So 300 add 70 they've both been made 10 times bigger will give me the answer 370. And for the last question here, a bit of a trickier one, as you need to do some regrouping. But the way I did it was I thought about my tens column, eight add three is 11, that gives me 110. And when I add that to the other hundreds that I've got there gives me 710. Okay, time for you to have a go. I've given you a little bit of help with the first one. Pause the video and take as long as you need to answer these questions. Okay, let's see how you got on then. So hopefully that helped you there with the first question of 140. So one add three in your tens column allows you to change that number to 140. And then we've got 290, 480, 160 and 820. Well done if you've got all of those right. So that last question, another bit of regrouping needed. If you think about the numbers in your tens column, you've got four add eight or eight add four doesn't matter which order you prefer to order them, that gives you 12. And then when you add that to the five and the two and if you think about 12 being 120 you end up with 820. Okay, so let's move on to rounding then and what we mean by rounding. So in this quick lesson, we're thinking about rounding to the nearest 10. So what we're saying is which multiple of 10 is each number nearest to. So think about the number 67. And what we do is we think about which two multiples of 10 it sits in between. So 67 is in between 60 and 70. Okay, It's there actually in between 60 and 70. If you think about this number line, it's split up into tens we've got 10 numbers between 60 and 70 and that's why 67 sits. The next thing we think about is which is it closer to 60 or 70? Well hopefully, you can see that it's closer to 70. And so when we round six to seven to the nearest 10, we get 70. Can you have a go? How would you round 32 to the nearest 10? I'm going to be kind and am going to give you the two tens that it sits in between. Pause the video here and work out what 32 rounded to the nearest 10 is. Now, here's where 32 sits. Hopefully, you can see that that's closer to 30 than it is to 40. Okay, What about a larger number then, a three digit number. We can still round this to the nearest 10 and we do it in a really similar way. And that we think about which two tens it sits in between. So 234 sits in between 230 and 240. It sits here between 230 and 240. And hopefully, you can see that that is closer to 230 than it is to 240. Have a go at this one, this three digit number. Think carefully about which multiples of 10 it sits in between and which one you think is closest to. Pause the video and have a go. Okay, let's see how you got on. Probably if you really got this far and you could see that 679 sits in between 670 and 680, 679 well it's closer to 680 isn't it? Like a 680 is the next number after 679. So rounded to the nearest 10, 679 is 680. So what we're doing is we're looking for the multiple of 10 that that number is closest to. That's what we mean when we say rounding to the nearest 10. So, some rules for you. If the ones in the ones column, if you've got one, two, three, or four, you round down. If you've got five, six, seven, eight or nine, you round up. Have a go. Pause the video here and round all of these numbers to the nearest 10. How did you get on? Here are your answers, have a look at how you did. Were there any mistakes you made at all? I wonder whether if you have made a mistake it's with that last one, 789. Sometimes it's harder with larger numbers to think about the multiples of 10 they sit in between. Think about your tens column, It's 780. So it must sit between 80 and the next multiple of 10, which is 90. Sometimes people get confused and go down one like it sits in between 770 and 780 Okay. 789 is between 780 and 790. Okay, Why are we doing this? Why are we rounding? Well, because what today's lesson is all about is estimating. That means that instead of writing down a calculation or taking a really long time to work out a calculation in your head, estimation can be useful for a whole number of things. And like I said at the beginning of the lesson, it's a good guess. So what we can do to make that good guess, that mathematical guess is round the numbers. I am, you know, this question would be tricky to do in our heads so we can round. So we can round both of them. We can round 36 to 40 and we can round 97 to 100. And if I do that, it makes it a much easier sum to add. 40 and 100 is much easier to add than 36 and 97. I can do it much more quickly. It doesn't give me a completely accurate answer. But It gives me a very good guess and it gets me somewhere near the right answer. So I could run both of them and that's the answer that I would get. But actually, it might be more useful to just round one of them. So if I just rounded 36 to 40, the sum I would have to do is 40 added to 96 which would give me 137. Or I could just around a 100, so 97 to 100. And that would give me the sum 36 add 100 is 136. And we can see that's a really easy sum to do. So looking at those three options, I think I'd get rid of the first option because I rounded both of them. And so I've taken both numbers away from their number. I think I might get rid of the second option as well, because 40 and 97 is still quite tricky sum to do. Whereas 36 at 100 is a very easy sum to do in my head. So if I see a number like 97 which is quite close to a hundred when I'm estimating I would probably think, yeah, I'm going to round that number to 100 because it's very easy to add numbers to 100. If we look at what the correct answer is, the accurate answer, the answer is 133. So you can say that's the first question I did. The first answer I did I've got 140 was the furthest away from the correct answer. Whereas they got more accurate as I went through. So you're going to try and round one of your numbers to make the addition questions more easy today. Okay, so pick which number you would like to round. Have a think about why you've chosen to round that number and then have a go at answering the question. Remember, I'm not looking for the absolute perfect answer. I want to see that you rounded one of the numbers and then added it in your head. Pause the video here and have a go. Okay, let's have a look at how you got on. I wonder if you'll working look like mine. Remember, I was hoping you would do this in your head but I'm just going to write it out to show the options that you might have. So, like I said you could round both of them, so we can round 23 rounds down to 20 and 59 rounds up to 60. And if we did that 20 add 60 is very easy to add together and it gives us the answer 80. You could do that very, very quickly. Maybe I just want to round 59 to 60 and the sum I would have to do then would be 23 add 60 gives me 83. Or I might just want to round 23 to 20. I think 20 add 59 gives me 79. Hopefully, you did one of the two bottom ones where you only rounded one of the numbers. The exact right answer is 82. You can see that last option gets you very close to the right answer, but actually both of them, sorry the middle one is really close as well. And that's because when you rounded 59 to 60, you've only moved 59 one digit to go from 59 to 60. You've only changed it by one, just by one. So that's very close to the completely accurate answer. Also, I think that's probably the easiest sum to do 23 add 60 is 83. But again, some of that comes down to personal preference. Okay, what about when we've got a three digit number then? So we need to choose which ones we want to round. We can around both of them but that will give us an answer that's quite far away from the accurate correct answer. So here I rounded both of them. What I'd like you to do is pause the video, choose to rounding one of them and have a go answering that question. Let's see how you did. If you chose just 360 or just 200, and let's see how you got on in getting a sort of as close to an accurate answer as possible. So if we just rounded 200, we'd have 357 add 200, which is quite a nice, easy sum to do. We know we only need to amend the hundreds columns. And that gives us 557 or we could end up with 360 add 197. I don't like that one at all. I find that very hard to do in my head. So the best option here to round 197 to 200. And like I mentioned in one of the earlier questions, if we can round to something to a hundred, it makes adding any number to it quite easy. So we got 557. The completely accurate answer is 554. So you can see that rounding is a nice way of getting us to very close to the right answer in the right ballpark. And we can answer it mentally. Here's one more for you to have a go at. Pause or the video and have a go. Hey, how did you get on? Which number did you choose to round? Well, here at both options for you, both numbers rounded. So hopefully, you had 110 or 530 in your working out. One of them gives you 639. The other one gives you 641. I personally think I'd probably, what would I do? I think there's not much in it for that one really Is it? 'Cause you can either have 530 or you can have 110. I'd probably go for 110 add 531, I think 110 is a nice easy number to work with. But that might come down to your personal preference. The correct answer was 640. So you can see that we're getting very close to the correct answer by rounding. And it allows us to do those calculations in our head rather than writing them out. Okay, it's that time of the lesson for you to pause the video take as long as you need to do the independent work and come back together for the answers. Okay, let's go through these answers together then. So you had some three digit numbers to round to start with, so let's see how you got on. So these are the right answers for rounding Well done If you've got all of those right a really good place to start. Of course that went well If you could see that eighty was the odd one out, you didn't need to do anything to it was already rounded. So here are some questions where I wanted you to round to estimate the answer. Now, our answers might differ because we might have chosen to round different numbers. That's absolutely fine as long as your answer is somewhere near mine. Mine is'nt right, they're both estimates. So, as long as your number is somewhere near the ones that are here then that's absolutely fine. The next question is really interesting 'cause we have these people here talking about which numbers they think they should round. Look at the ideas and decide which one's best. Now the best one is this one here which appears in Blue. Now, they decided to round 32 to the nearest 10. 32 only needs to go down two to round to the nearest 10. This one also gives you quite an accurate answer but it's really the blue one which is best. The green one doesn't give you a very accurate answer at all. And also they haven't rounded very well rounding to the nearest 100 would give you quite an inaccurate answer for that one. So well done. If you could get one of those right Now's the time for that final knowledge quiz to see how well you perform with today's lesson. Lots of new learning today. So really well done for sticking with it. And have a fantastic day for the rest of your learning. Bye bye.

Let's see what you have about rounding to estimate today

Which of numbers does not need to be rounded to the nearest 10?

What is 27 rounded to the nearest 10?

What is 523 rounded to the nearest 10?

Round to estimate this answer 102 + 45 =

What is 1999 rounded to the nearest 10?

Applying Rounding to Estimate (Adding) Quiz

In this lesson, we will build on our knowledge of the 10 times table in order to estimate by rounding.  We will do this to answer addition questions.

Maths

Y3 Maths

Key Stage 2

Year 3

Applying rounding for estimating (adding)

Addition and subtraction

Number

THEME

UNIT

Adding and subtracting 1-digit numbers to/from 3-digit numbers

Adding multiples of 10 to 3-digit numbers

Subtracting multiples of 10 from 3-digit numbers

Adding and subtracting multiples of 100 to/from 3-digit numbers

Adding two 3-digit numbers (without regrouping)

Subtracting two 3-digit numbers (without regrouping)

Applying rounding for estimating (subtracting)

Adding two 3-digit numbers (regrouping in one column)

Adding two 3-digit numbers (regrouping in multiple columns)

Subtracting 3-digit numbers (regrouping tens to ones)

Subtracting 3-digit numbers (regrouping hundreds to tens)

Subtracting 3-digit numbers (regrouping in multiple columns)

Solving addition and subtraction word problems

Solving word problems with unknown values

Tia is looking after the neighbour's dogs. The adult dog eats 450 g more than the puppy. If the adult dog eats 875 g how much will the puppy eat?                            Does this question need addition or subtraction to answer it?

Which question would this bar model help to answer?

Before the final rounds of races on sports day, the green team had 372 points. They ended up winning the competition with 518 points altogether. How many more points did they make in the final round?

222 + 7 =

308 + 8 =

Does this look like a good estimate? 720 - 30 = 500

Edinburgh castle sold 345 tickets for tours on Monday. On Tuesday it sold 109 less. How many tickets were sold on Tuesday?

Lesson overview:Applying rounding for estimating (adding)

Core Content

Addition and subtraction: