SLCN Lesson Three Addition Algorithm

Transcription

1 SLCN Lesson Three Addition Algorithm LESSON THREE Stage Two Addition Algorithm Introduction: Provide a statement of goals What we re going to be learning about today is about adding numbers. We re going to be looking at a special way of doing that today. We re going to be looking at an algorithm. OK? Now the algorithm has been around for a long time. I m sure your parents learnt how to do this algorithm and it s a method that we use that will pretty well always get us the right answer when we use it. Introduction: Review previous learning Before we start looking at this algorithm I just want to make sure that you guys understand about numbers and how numbers work. On this mat we ve got a place value board. So we ve got the ones column, the tens column and the hundreds column and I know you all are very familiar with that because you ve worked with those a lot. OK. I ve represented a number, I ve actually made a number that you can see on that place value board and I m sure you all know that that number is... you can say it for me. Twenty three. Strategy Watch symbolic to concrete representation Twenty three. Excellent and I m going to write that number up here on the board. Give clear and detailed instructions and explanations Now there are special rules with this algorithm and we re going to be talking about those today and the first rule is that we always start with the ones and the second rule is that we can t have more than nine in any column. OK? So they re the two rules that I m going to Online Training Ltd Page 1 of 5

2 see if you can remember at the end of the lesson and we ll be talking about those a lot today. Give clear and detailed instructions and explanations Let s have a look at fifty-fife. Who can make fifty-five for me? Someone who hasn t had a turn. OK. Come on. You can use my blocks and you re going to make fifty-five. Now they re already tens so you don t need to worry about those. OK, good. We might just move them up because we re going to put another one. And that s fine to have them like that. It doesn t matter which way round we have them does it? They re still whole tens. OK, so fifty-five. We re going to add on this number. OK? We re going to add on sixty-six so we ve got our fifty-five represented here and I m going to move them up so we ve got room for our sixty-six and I m going to choose somebody to make sixty-six and put it underneath the fifty-five, just the way we have it here on the board. OK? Have you had a turn? Come on. And there s six for you. Thank you very much. OK, great, so we ve got fifty-five and we might match them and put them like that and we ve got our fifty-five at the top and our sixty-six at the bottom. We re going to show on the place value mat here and on the board how we add those numbers together. OK? Now I know you know the answer to this one. Where do we start? Everyone. One! (children call out) We always start with the ones, don t we? OK, so we ve got five ones and six ones which makes eleven ones. Strategy Present new material in small steps OK, am I allowed to put eleven down here? No. Because what s the biggest number I can have in that column everyone? OK, so I have to trade ten of those ones for one ten and I have to move it into the tens column. So let s just do that. Eight, nine, ten. And where am I going to put it? In the tens column! Strategy: Match symbolic to concrete representation In the tens column up the top. OK. So let s do that up here. Online Training Ltd Page 2 of 5

3 Strategy: Match symbolic to concrete representation Let s show everybody what we did up here. I haven t got a lot of room. I should have left myself more room but we put the ten can you all see that little ten up there - in the tens column. OK, so we ve added five and six which is eleven ones, we traded ten of those for a ten and put it into the tens column. So what number am I going to write here? One! Excellent. One. OK. So now we ve got one ten and five tens and six tens. What does this column add up to? Hands up please. Twelve. Five and six and one adds up to twelve tens. That s right. Now can I put twelve tens at the bottom in my tens column? Now you know we can t do that because the biggest digit we can have in any column is? Nine, absolutely. So if this adds up to twelve tens, what am I going to do? What do I have to do? It adds up to twelve tens, what do I have to do? Put ten of those tens in the hundreds column. Strategy: Model correct language We re going to trade ten of those tens for a one hundred. So how many tens do I need to make a one hundred? Ten! Absolutely. OK. So now I have organised ten of my tens into a one hundred and where am I going to put it? In the hundreds column! In the hundreds column. Excellent. OK. So we ve got twelve tens. I traded ten of them for a one hundred and it has to go up into the... Hundred!...hundreds column and what am I going to write here? Two! Online Training Ltd Page 3 of 5

4 Two tens. And then what am I going to write here? One! And I have to remember to include that one hundred. Excellent. So the answer is? One hundred and twenty one! One hundred and twenty one. Provide high levels of practice Guide students through initial practice Now, remember, the question is do we need to do any trading to complete that algorithm? Do we need to do any trading to complete that algorithm? Yes, yes. Why? Because six and five add over nine. Excellent. Because we start with the ones and six and five ones is eleven ones. So we can t put eleven down here because we can t put any number bigger than... Excellent. Strategy: Provide non-examples Have a look at the last one and remember, the question is, do we have to do trading? Do we have to do trading? Yes? Hm... yes. OK, why don t we have to do trading? Because it s nine. OK, because we start with the ones and two ones and seven ones makes nine ones. We re allowed to have nine there aren t we? We re allowed to have nine, exactly. So it s nine ones, three tens and one ten makes four tens. So the answer is forty-nine. Provide high levels of practice Provide systematic feedback and corrections Online Training Ltd Page 4 of 5

5 All right, now just before you go further, Sean, OK, let s have a look at thefirst one that you ve done. You re nice and fast aren t you, you re able to do this. You ve got four ones and seven ones which is... Eleven. Eleven ones. OK. So I can see that you ve traded ten of those ones for a ten. But remember we talked about where to put that ten. OK. We need to put it right on top of the other tens so that it sits there, otherwise you might get confused and think that s a different number. OK? So could you remember in the next one to make sure that when you trade those ten ones for a ten that you write that ten right on the top of the other ten? OK? So let s see you doing it in that way. Conclusion All right, that was really great work 3/4. I was quite impressed with the work you were doing. So what have we been learning about today? We ve been learning how to do...? Trading additions! We ve been learning how to do addition algorithms, that s great, and we ve been learning how to trade, that s right. So we ve been learning the method of addition of the written addition algorithm and we ve been learning about when to trade so let s just try and remember, and I m sure you can, those two rules that we talked about at the very beginning. What was the first rule when you re adding numbers using the written algorithm? What s the very first rule Jeremy? You don t have any number larger than nine. OK, that was the second rule. You can not have any number in any column larger than nine. OK, so Jeremy gave us the second rule. And what was the first rule? Start at one. Always start with the ones. Excellent. So who remembered that the whole time? Great, hands down. That s terrific. Thank you. Online Training Ltd Page 5 of 5