Addition within 20
Current time:0:00Total duration:3:19
Voiceover:Let's try to think about what 8 plus 7 is equal to. And we could imagine that this is like taking 8 tomatoes and adding 7 blueberries and then saying, "How many pieces of fruit "do you have in total?" I encourage you to pause the video and try this out on your own. So, I'm assuming you've given a try. So let's think about it a little bit. And the way I'm going to think about it is, I'm going to keep adding tomatoes until I fill up my first bucket of 10 and then I'm going to see how many more I have to add to get, to essentially, add a total of 7. So let's have 1 tomato, 2 tomatoes, 3 tomatoes, 4 tomatoes, 5 tomatoes, 6 tomatoes, 7, and 8 tomatoes. Now, to those 8 tomatoes I'm going to add 7 blueberries. So that's going to be 1, 2 ... And actually, I'm going to pause there. Because I just finished a group of 10. This, right over here, I've only added 2 of the blueberries. I still have some more blueberries to add, but just with adding those 2 blueberries, I have completed a group of 10. So I already have 10 pieces of fruit. So I can represent that. I know, since I have a group of 10 here, that I have 1 group of 10. So this is going to be a 2 digit number, where the digit on the left is going to be a 1. But I'm not done adding blueberries. I've only added 2 blueberries. Now let me add a third. 3 blueberries, 4 blueberries, 5 blueberries, 6 blueberries, and 7 blue berries. So I have a group of 10 and then, above and beyond filling out that group of 10, which is represented here, because this is going to be a 2 digit number. This is the left digit. So this 1, since it's in the tens place, it literally represents 1 group of 10, which is right over there. And then how many more do I have? Well I have another ... I have another 5, 1's. 5, 1's right over here. So we have 1, 10 and we have 5, 1's. So what is 8 plus 7? It is 15. And another way, just to remind ourselves what 15 represents. The 1 in 15 represents 1, 10. Let me write it down. It represents, it represents 1, 10. And the 5 represents 5, 1's. 5, 1's. And so another way of thinking about it, 1, 10 is the same thing as 10 and 5, 1's is the same thing as 5. So 8 plus 7 is 15. That was the whole point of this video. But we also want to think about what these numbers represent. 15 literally represents 1, 10 plus 5, 1's. Or 10 plus 5.