﻿Hello again, it's Mrs. Judith here. And I'm going to be taking your lesson today. Let's go through the practise activity that I left you last lesson. Did you notice anything about the equations? Can we use our generalisations to help us solve them? If we have a look at six plus one, we know that adding one gives one more and one more than six is seven. And then if we look at the equation next to it, we can see that it's just that the order of the addends has been changed. So we know that when we change the order of the addends, the sum remains the same. So one plus six is seven. Five plus one, one more than five is six. And we can see on the opposite equation that we have just changed the order of the addends, but the sum remains the same. And then we've got this one here, four plus one. One more than four is five. And there we've just changed the order of the addends in the next equation, so that is also five. Zero plus one. One more than zero is one and one plus zero is also one. Here's our number line again. this time we're going to start counting backwards. So we're going to start on 10. Do you think you can help me? Are you ready? Here we go. 10, nine, eight, oh, nine, there's a number missing. Did you say the right number? What's one less than eight? Did you say seven? Fantastic, six, five, I've got another missing number. One less than five, what's one lesson five? Did you say four? Well done, four is one lesson five. Three, two, one, zero. Great counting, we're going to be using this, to help us solve some problems today. Do you think you could tell me to tell this story today? What can you see in the picture? Pause the video if you need to. So we could say first there were eight donut. Then what happened? Could you pause the video and tell an adult or you can tell me what happened next? Then someone took her donut. Someone took one away. Now how many are left? What will the equation look like that goes with this story? Have a think. So we've got eight donuts first of all, first we had eight. Minus one is equal to, wow, I know that seven is one less than eight. So eight minus one must be seven. Eight minus one is equal to seven. What does the eight represent in this equation? That's right, the eight represents the eight donuts I had first of all. What does the one represent? Yes, the one represents the one donut that has been taken away. And what does the seven represent? The seven represents how many donuts are left now. Did you notice something? I can see that when I subtract one the difference is one less than the minuend. We could also represent this equation with a bar model. What would go where the question mark is? Did you say seven? That's right because eight minus one is equal to seven. And remember when I subtract one I can see that the difference is one less than the minuend. Seven is one less than eight. Can you help me to tell this story? First there are five counters. Then I take one away. Now that are? What's the equation that goes with this story? Five minus one is equal to four. I know that four is one less than five. What does the five represent in this equation? The five represents the five counters that I had to start with. What does the one represent? The one represents the one counter that I took away. And what does the four represent? That's right, the four counters that I have left and I know that one less than five is four. I also can see that when I subtract one the difference is one less than the minuend. How many pens are in this picture all together? Pause the video if you need to count them. Did you say that there are seven pens all together? And how many of those pens are orange? That's right, one of the pens is orange. So what would the equation be to find out how many pens are blue? Have a think. Did you say that I would need to do seven minus one, seven minus one? Well, I know that one less than seven is six. So I can say that six of the pens are blue. What does the seven represent in this equation? That's right, the seven represents the seven pens that we have all together. And what does the one represent? Yes, the one represents the one orange pen. And what does the six represent? That's right, the six represents the six blue pens. I can show this problem using a part-part-whole model. What's my missing number though? Did you say six? That's absolutely right. And can you remember that when I subtract one I can see that the difference is one less than the minuend. How many counters are there all together? That's right, there are five counters all together. And how many of the counters are blue? Yes, one of the counters is blue. So what would the equation be, to work out how many red counters there are? Did you say that I would need to do five minus one and what's that equal to? That's right, one less than five is four. So five minus one is equal to four. What does the five represent? Yes, the five represents the five counters I have all together. And what does the one represent? The one represents the one blue counter. And what does the four represent? Yes, the four represents the four red counters. And I know that when I subtract one the difference is one less than the minuend. I can also represent this problem using a part-part-whole model. What would go in the missing part? That's right, it would be the four. What does the four represent? Yes, the four red counters. What does the one represent? The one blue counter. And what does the five represent? Yes, the five counters all together. So if we know that subtracting one gives one less, I bet we can answer these questions really quickly. We also know that when we subtract one the difference will always be one last than the minuend. Should we see if we can do these together really quickly. I'm going to say the first part of the equation, and I would like you to say the difference. Are you ready? 10 minus one is equal to, nine. Nine minus one is equal to, eight. Eight minus one is equal to, seven, yeah. Five minus one is equal to, four. Four minus one is equal to, three. Three minus one is equal to, two. That's fine, I bet you did them really quickly. You're getting really good at this. I want you to have a go at these questions now. Pause the video, you can either just say them or you can write them down if you would like to, but look carefully. Are they all subtraction equations? Hey, that's right, some of them are addition. Remember, subtracting one gives one less and adding one gives one more. Pause the video now and have a go at these. Did you have a go at them? I bet we can do them really quickly. We're going to say the equation together. Are you ready? Three plus one is four. One plus nine is 10. Four plus, oh, this one's a bit different. This time one of the addends is missing. Four plus mmh, is equal to five. Well, I know that five is one more than four. So the missing addend must be one. Four plus one is equal to five. Oh, let's have a look now, it's the sum that's missing. One plus one, so that must be two. Two is equal to one plus one. The sum is missing in the next equation as well. But one more than five is six. So six is equal to one plus five. Now I've got my first addend missing. Mmh plus one is equal to eight. That must be seven, because seven plus one is equal to eight. Now I'm doing some subtraction. So nine minus one, well I know one less than nine is eight. Oh, this is a bit tricky. One minus one. But one less than one is zero. Let's have a look at this last one. Seven minus mmh is equal to six. But I know that six is one less than seven. So the missing number must be one. Seven minus one is equal to six. You've worked really hard today and you're getting really good at this. I want you to have a go at these two word problems now. I want you to think about what equations would go with each question, there might be more than one equation. And can you draw a bar model or a part-part-whole model to go with this? So question one says, I find one conker in the playground. I pick up six more on the way home. How many do I have now? Can you write the equations that go with that question and draw a bar model or part-part-whole? Then question two. I challenge myself to swim four width of the pool. I have swum one width. How many more widths do I need to swim? Again can you write the equations that go with this problem? And can you draw a bar model or a part-part-whole model to go with it? Well done for all your hard work this time.

In this lesson, we will learn that subtracting one gives one less.

In this lesson, we will learn that subtracting one gives one less. Resources provided by NCETM (CC BY-NC-SA: https://creativecommons.org/licenses/by-nc-sa/4.0)

Lesson overview:Subtracting one

Core Content

Addition and Subtraction: