Which one of these shows a number bond to 20

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

Key Stage 2

Maths

Addition and subtraction

﻿Hello everyone. I'm Miss Brinkworth. I'm really excited to go through this math lesson with you today. If we look at our learning objectives, we are adding or subtracting one digit numbers from three digit numbers. So let's have a look at our lesson agenda for today. We're going to be revisiting some strategies that you've probably used before in terms of adding and subtracting. We then going to move on to a mental strategy called making 10. So using that knowledge, you've got to have numbers that add up to 10. We'll also look at number bonds to 20 and how that can help us with adding and subtracting from these larger numbers. And you'll have an opportunity for some independent work, followed by that exit quiz at the end, where you can see how well you've got on with today's learning. All you're going to need is a pen or pencil, something to write on, and a great attitude. We're going to have a really, really good lesson. Okay. For a warm up, there are some really simple and just efficient question for you here. And, you'll probably be able to answer these questions really quickly in your head, but what I'd really like you to do is think about the strategy that you've used, what have you actually done to add those numbers together? Think if you'd like about explaining what you've done to a younger child. Sometimes when we go through mental calculations really quickly, it's quite difficult for us to stop and think about how we did it. So answer one or two of these questions only, but really think carefully about what it is you did, what knowledge you used to answer those questions. How did you get them? And, like I said, it can be quite tricky to slow down and think about what it is you've done. So let me have a go explaining what I mean. I picked this question, 35 add three. And I know that the answer is 38. So how do I know that? What did I do to work that out? Well, I just added together the numbers in the ones column, five add three is 8, so thirty five add three is 38. For another one of the questions like 67 add five, I might have to do something slightly different. What I did here was that I split five down into three and two. I did this because I know that seven add three is a number bond that takes me to the next lot of 10. So 67 add three, is 70. And then I just need to add the other two that's left over from the five, to give me the answer of 72. I wonder if you used any strategies like that when you were answering these questions, or if you used completely different ones, that's fine as well. Let's have a look then. Today, we've got questions like this word problem, and we need to pull them math out of it and think carefully about what it's asking us. What we know from the question, and what we need to work out. So let's have a look together. One Monday morning, there had been 326 visitors to Edinburgh Castle. Just before 12 o'clock, a family of five also arrived at the castle. How many visitors were there all together on Monday morning? So what do we need know? We know that we had 326 visitors, and then five visitors. And we know that the question is asking us, how many were there all together. So, a bar chart or bar and picture, can help us, and a bar model, sorry, can help us work out what we know, and what we need to work out. So, we've got those two numbers there, 326 and five. So along the bottom we've got what we know. At the top where there's that question mark, that's what we're trying to work out, that's our unknown. And this bar model makes it clear that this is an adding question. We need to add those two amounts together to find the total. Okay, how do we do that then? So here's our question 326 add five. And I'm going to show you two different ways that you might answer this question. They are both going to get the same answer but they are slightly different strategies. So the first one is that make ten strategy I was talking about. So this is where, we might split five down into four and one. Why do you think we might split five into four and one? Well, the reason is because if I look at the ones in my three digit number, they're right at the beginning, 326, six and four are a number bond which takes me to 10. So if I add four onto 326, I get 330. And then I've just got one more to add on to 331. So we can split the number down, and, make those make 10 strategy there. Another thing you might want to do, a different strategy, is actually number one to 20. So this time, I'm splitting my three digit number. I'm splitting 326 into 320, and six. I then, can add six and five, six and five is 11, and then add those two numbers together, 320 and 11 and 331. As you can see, both of these strategies get me to the same answer. It's just about which one you prefer, or which one you think suits the question better. So just to recap these two strategies, we might want to split down the one digit number, and think about making 10 with the three digit number, and then add on the the other bit as well. Or, we might want to think about number bonds to 20, and split up our three digit number, make number bonds to 20, and then add them back together. So, your choice, have a go at these questions, decide which strategy you would like to use. Pause the video, we'll come back together in just a moment. How did you get on? I wonder if there was some that when you looked at, you were happier about answering really quickly, and others that you thought you might need a bit more time. We all have preferences when it comes to the questions that we answer and that's absolutely fine. In fact, it can be really useful to think about why you prefer certain numbers. Is it because you find adding them or subtracting them slightly easier? I wonder if you preferred it when the three digit number was at the beginning, or at the end of the question? We know that with adding, it doesn't matter which order we add two numbers in, but for your own personal preference, if you prefer it one way or the other, you know you can move them around. So, I'll put the answers up and I won't spend too much time going through them. They're there for you to see whether you've got those right or not. And I'm really hoping that you use those strategies the make 10, the number bonds to 20 as well. Also as well, it's just worth noting that when we're talking about adding questions, we would of course expect our answer to be bigger than either of the numbers we were adding, because we've taken two numbers and putting them together. So we would expect the answer to be bigger. It's really worth checking your answer, and just making sure that it looks reasonable. So it's bigger than the numbers you started with, but it sounds reasonable with the two numbers that you did start with. Okay. Here's another word problem then. That Edinburgh castle gift shop had 223 postcards in stock. A visitor bought six of them, how many were left in the shop? So this time, we had an amount and some have gone, how many were left? So it's not an adding question, but the bar modelling can still be really useful for us to show us what we know, and what we don't know. This time, we know the big number that we started with, we know the number that's been taken away, and what we don't know, is how much we've been left with. So what might our strategies be? 223 takeaway six. What would you use? I know that's what I would use. Where does your mind go when you look at this question, I wonder? Well, let's have a look. You can use the same similar strategies, the ones that we've already talked about. So again, you can split your three digit number up into 210 and 13. Then you can do 13 take away six is seven, and then put that back in to give you 217. Or, this is the one I prefer I think. You can split six down into three and three. You can take away one three, and then take away another three. So 223 takeaway three is 220, and then just to go back three more, gives us 217. So we've got those two different strategies in play there again. And you can partition either number to help you with the answer. I'll just leave those there for a moment. I wonder which one you prefer. Okay, so let's have a look at this slide together and use our addition and subtraction strategies to work out what's going on. Have a look at this nine square and see if you can work out what the rule is, what is the relationship between these numbers in this square? Have you been able to spot? Well, hopefully you can spot that the numbers on each side add up to make the number in the middle. So if we look at that row across the top, 218 add seven gives us the 225, in the middle. Moving down one, six and 325 gives us 331 in the middle. So we need to work out what that missing number is. What is it that I need? What is added to four that gives us 232? So we need to think about whether this is an addition question, or a takeaway question. Well, the way I'm going to work that out is that I know I'm going to get a smaller number than 232. Because the numbers on the side are smaller than the ones in the middle. So what I need to do is 232 take away four, subtract four. And the strategy I'm going to use to do that is to partition four into two and two. Why do you think I'm going to partition my four into two, and two? Well, that's because the number that I'm taking it away from 232 has got that two at the end. So if I take away two, and then I take away another two, I'm going to find that quite easy to do in my head mentally. So, 232 take away two, is 230. 230 take away my last two, gives me the answer of, 228. Well done if you could see that. Okay, now it's that time of the lesson for you to have a go at your independent task. So pause the video here and then come back together for the answers. How did you get them? Let's have a look at these questions together. So, this says you can pick any mental strategy. So hopefully you've been able to use those strategies of making 10 or partitioning and using our numbers bonds to 20. So here are the answers. I'm not going to go through in a lot of detail but they are there for you to see how you got them. I wonder if you could see any similarities between the questions that you were asked to answer using certain strategy. If you were able to pick those into different categories. Okay, having a look at this last challenge then, and this was similar to the one we just looked at just before the independent work, and we need to think about the relationships that are going on here. So, if we look at that first square on the left, we can see it's the same as the one we looked at just before the independent work, where the numbers on each side are smaller than the numbers in the middle. So it must be that we add the numbers from the sides to give us the number in the middle. So what we need to do is add six to 237. So what was your strategy for doing that? I'm going to split six up into three and three. I'm going to do that because I know that seven and three are a number bond. So, if I add my three onto 237, I'm going to get 240. And then I need to add another three to get me the answer, of 243. Okay, what about the next one then? Does it follow the same rule? Is the largest number in the middle? It's not is it? The largest number is actually at the end this time. So it must be that we add the first two columns together to give us the answer in the last column. So what is it I need to add to five to get to three hundred and forty two? What do I need to add to five to get 342? Well, to work that out, I could take five away in 342. I'm going to partition my five into two and three, so that I can take the two away to get me to 340, and then I can take the three away, and get the right answer of 337. Really well done if you're getting these ones right, these aren't too easy, really good work. Okay, so for the final one then. In what pattern is this one following? Well again, it looks like the largest numbers right at the end. So we're adding together the first two columns to give us the one at the end. So what do I need to add to seven to get me 553? Well, again, I can take my seven away from 553 to get me the answer. And again, I really like doing partitioning when you can see a question like this. So I'm going to partition my seven into three and four, take away the three which takes me down to 550 and then take away the four gets me to 546. Really well done if you got all of those right. Okay. Remember that if you'd like to please ask your parent or carer to share your work on Twitter, tagging @OakNational and #LearnwithOak. And now's the time for you to do your quiz and see how well today's learning has gone on. Really good work everybody. Well done. Bye bye.

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

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

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UnitMaths / Addition and subtraction

Maths