Arithmetic (all content)
Introduction to addition. Learn multiple visual ways to represent addition. Created by Sal Khan.
Welcome to the presentation on basic addition. I know what you're thinking, Sal, addition doesn't seem so basic to me. Well, I apologize. Hopefully by the end of this presentation or in a couple of weeks it will seem basic. So let's get started with, I guess we could say, some problems. Well let's say I start with an old classic. 1 plus 1. And I think you already know how to do this, but I'll kind of show you a way of doing this in case you don't have this memorized or you haven't already mastered this. You say, well, if I have 1, let's call that an avocado. If I have 1 avocado and then you were to give me another avocado, how many avocados do I now have? Well, let's see. I have 1, 2 avocados. So 1 plus 1 is equal to 2. Now, I know what you're thinking. That was too easy, so let me give you something a little bit more difficult. I like the avocados. I might stick with that theme. What is 3 plus 4? This is, I think, a more difficult problem. Well, let's stick with the avocados. And in case you don't know what an avocado is, it's actually a very delicious fruit. It's actually the fattiest of all the fruits. You probably didn't even think it was a fruit, even if you ate one. Let's say I have 3 avocados-- 1, 2, 3. And let's say you were to give me 4 more avocados. So let me put this 4 in yellow so you know that these are the ones you're giving me. 1, 2, 3, 4. So how many total avocados do I have now? That's 1, 2, 3, 4, 5, 6, 7 avocados. So 3 plus 4 is equal to 7. And now I'm going to introduce you to another way of thinking about this. It's called the number line. And actually, I think this is how I do it in my head when I forget-- if I don't have it memorized. So number line, I just write all the numbers in order. And I go high enough just so all the numbers I'm using are kind of in it. So you know the first number is 0, which is nothing. Maybe you don't know, but now you know. And then you go to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Keeps going-- 11. So we're saying 3 plus 4. So let's start at 3. So I have 3 here and we're going to add 4 to that 3. So all we do is we go up the number line, or we go to the right on the number line, 4 more. So we go 1, 2, 3, 4. Notice all we did is we just increased it by one, by two, by three, by four. And then we ended up at 7. And that was our answer. We can do a couple of different ones. What if I asked you what 8 plus 1 is? Well, you might already know it. You know, plus 1 is just the next number. But if we look at the number line you start at 8 and you add 1. 8 plus 1 is equal to 9. Let's do some harder problems. And just so you know, if you're a little daunted by this initially, you can always draw the circles. You can always do the number line. And eventually, over time, the more practice you do-- you'll hopefully memorize these and you'll do these problems in like half a second. I promise you. You just got to keep practicing. I want to draw the number line again, actually, I have a line tool, so I should give you all those ugly looking lines that I've been giving you. Look at that. That's amazing. Let me see. Look at that. That's a nice looking line. I'm going to feel bad to erase it later on. So let me draw a number line. 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15. So let's do a hard problem. I'm going to do it in different colors now. 5 plus 6. So if you want, you could pause the video and try this. You might already know the answer. And the reason why I say this is a hard problem is because the answer has more numbers than figures, so you can't necessarily do it on your fingers. So let's get started with this problem. Actually, my phone is ringing, but I'm going to ignore the phone because you're more important. OK, let's start at the 5. So we start at the 5 and we're going to add 6 to it. So we go 1, 2, 3, 4, 5, 6. And we're at 11. So 5 plus 6 is equal to 11. Now I'm going to ask you a question, what is 6 plus 5? Well, we're now going to see that. Can you switch the two numbers and get the same answer? Well, let's try that. And I'm going to try it in a different color so we don't get all confused. So let's start at 6. Ignore the yellow for now and add 5 to it. 1, 2, 3, 4, 5. We get to the same place. And I think you might want to try this on a bunch of problems and you'll see it always works out. That it doesn't matter what order-- 5 plus 6 is the same thing as 6 plus 5. And that makes sense. If I have 5 avocados and you give me 6, I'm going to have 11. If I have 6 avocados and you gave me 5, I'm going to have 11 either way. Since this number line is so nice, I want to do a few more problems using it. Although as I use it I'm sure I'll just continue to confuse you because I'll write so much on top of it. But let's see. I'll use white now. What is 8 plus 7? Well, if you can still read this, 8 is right here. We're going to add 7 to it. 1, 2, 3, 4, 5, 6, 7. We go to 15. 8 plus 7 is 15. So hopefully that gives you a sense of how to do these types of problems. I guess this and you're going to learn multiplication in a little bit, but these types of problems are-- when you're getting started off in mathematics, these kind of require the most practice and to some degree, you have to start memorizing them. But over time, when you look back, I want you to remember how you feel while you're watching this video right now. And then I want you to watch this video in like 3 years and remember how you felt when you're watching it now. And you're going to be, oh my God. This was so easy because you're going to learn it so fast. So anyway, I think you have an idea. If you don't know the answer to any of the additional problems that we give in the exercises you can press the hints and it'll draw circles and you can just count up the circles. Or if you want to do it on your own so you get the problem right, you could draw the circles. Or you could draw a number line like we did in this presentation. I think you might be ready to tackle the addition problems. Have fun.