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# Adding 8 + 7

Sal adds 8 + 7 by making a group of ten. Created by Sal Khan.

## Want to join the conversation?

- What is the importance of Adding?(19 votes)
- Math is a way to analyze complex problems and the world around you. It helps your brain connect pathways and come to quicker solutions by breaking down a problem to its most basic ingredients (first principle thinking). It's only when you're able to break down a problem to its most fundamental components, you're able to see the solution. In math, we do this by using an abstract language (numbers)

Example:

8 + 7

10-8=2

7-2=5

10+5=15(13 votes)

- How big is the universe? Is it infinite?(6 votes)
- It is most probably finite, but constantly expanding, meaning that the galaxies are generally drifting apart from each other.(7 votes)

- I'm just here to study for my test even I'm in 5th grade XD my math teacher keeps say STUDY FOR TEST! I'm like srsly ;-;

<3(4 votes)- You can learn in 5th grade math. https://www.khanacademy.org/math/cc-fifth-grade-math(4 votes)

- I have eight bears. I gave some to Clara. Now I have 4 bears. How many did I give away?(3 votes)
- you now have 4 dangerous bears(2 votes)

- Is 7+3+5 an equation that can be used to get 7+8?(2 votes)
- That's another way of looking at it, yes. You could start at 7+3+5, then go (7+3)+5 so that you get 10+5, which equals 15. You could also go the other way with it, 5+2+8 -> 5+(2+8) -> 5+10 = 15.(5 votes)

- what would be 20 plus 900 plus 150(0 votes)
- Work it out: start with 900 + 150 = 1050. 1050 + 20 = 1070

Your answer is 1070(6 votes)

- why do we need to learn this... i mean isn't having fingers is to count?

please explain i feel like i am 6 years old(2 votes)- Well, it will become useful later in life. Try using your fingers to add 65,465+56,349(3 votes)

- So I'm a little bit confused about common core. What has changed, and how can I help my brother with it? Is there good information somewhere? Their website seems rather vague.(3 votes)
- Common core exercises and courses can be found here: https://www.khanacademy.org/commoncore(2 votes)

- how long should the lessions take(3 votes)
- I agree with Muhammad_Asif. Usually in school overall, I can finish my assignments very quickly, but my brother has more trouble succeeding. It's because I can learn quickly, and my brother has a harder time. The same applies to these lesson. It might be really easy and take a minute, tops, or it might be really hard and take an hour for you to master. If you want to figure out your rate of time, you can set a stopwatch and see how long it takes to do your next lesson, and then do the same with several lessons afterwards, and figure out what's closest to the center.(3 votes)

- Cant you just do 7 + 3+ 5 ?You could go to every ten.(3 votes)

## Video transcript

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.