Intro to addition and subtraction
Basic Addition Introduction to addition. Multiple visual ways to represent addition.
⇐ Use this menu to view and help create subtitles for this video in many different languages.
You'll probably want to hide YouTube's captions if using these subtitles.
- 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.
- I hope I --
- Hopefully, by the end of this presentation,
- or in a couple of weeks, it will seem basic.
- So lets get started with,
- I guess we could say, some problems.
- Well, let's say I start with an old classic.
- 1 + 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
- one
- (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 + 1 is equal to 2.
- Now, I know what you are 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 + 4?
- Hmm. 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, 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 [have eaten] one.
- So, let's say I have 3 avocados.
- 1, 2, 3. Right? 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 + 4 is equal to 7.
- And now I am 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 [on the] number line, I just write all the numbers in order,
- and I go high enough just so I can --
- [so that] all the numbers I am 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 (one)
- 2 (two)
- 3 (three)
- 4 (four)
- 5 (five)
- 6 (six)
- 7 (seven)
- 8 (eight)
- 9 (nine)
- 10 (ten)
- It keeps going,
- 11 (eleven)
- So, we're sayng 3 + 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 1, by 2, by 3, by 4.
- And then we ended up at 7.
- And that was our answer.
- We could do a couple of different ones.
- We could say, what is --
- What if I asked you what 8 + 1 is?
- Hmmm. 8 + 1.
- Well, you might already know it.
- 8 + 1 is just the next number [after 8].
- But if you look at the number line, you start at 8,
- and you add 1.
- 8 + 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've just got to keep practicing.
- Let's say....
- I want to draw the number line again.
- Actually, I have a line tool;
- so I shouldn't give you all of those ugly looking lines
- that I've been giving you.
- Look at that. Look at that. That's amazing.
- Alright, let me see.
- Oh. Oh. Yeah, look at that.
- Okay. So, that's a nice looking line.
- I'm gonna 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.
- What is --
- I'm gonna do it in different colors now.
- 5 + 6
- So if you want, you can 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 [is] more [than the]
- [number of fingers you have on your two hands].
- 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.
- So. Okay. Let's start start at the 5.
- So we start at the 5.
- And we're gonna add 6 to it.
- So we go: 1
- 2
- 3
- 4
- 5
- 6
- We're at 11!
- So 5 + 6 is equal to 11.
- Now I'm gonna ask you a question.
- What is 6 + 5?
- Huh...
- Well, we're now going to see that, OK?
- Can you switch the two numbers
- and get the same answer?
- Well, let's try that.
- I'm gonna try it in a different color,
- so we don't get all confused.
- So let's start at 6.
- Right? Ignore the yellow for now and add 5 to it.
- 1 ... 2 ... 3 ... 4 ... 5.
- Ah. 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 in what order you --
- "5 + 6" is the same thing as "6 + 5."
- And that makes sense.
- If I have 5 avocados and you give me 6,
- I'm gonna have 11.
- If I have 6 avocados and you gave me 5,
- I'm gonna have 11 -- either way.
- Let's do a couple of --
- Since this number line is so nice,
- I wanna do a few more problems using it.
- Although, as I use it,
- I'm sure I'll just continue to confuse you,
- 'cause I'll write so much on top of it. But --
- Let's see. I'll use white now.
- What is -- What is 8 + 7?
- Well, if you can still read this, 8 is right here.
- Right? We're gonna add 7 to it.
- 1 ... 2 ... 3 ... 4 ... 5 ... 6 ... 7.
- We go to 15.
- 8 + 7 is 15.
- So hopefully, that gives you a sense
- of how to do these types of problems.
- And more than, I guess this --
- and you're gonna 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, you know, when you look back,
- I want you to remember how you feel
- while you are watching this video right now.
- And then I want you to watch this video in, like, three years.
- And remember how you felt when you're watching it now.
- And you're going to be, "O my! This was so easy!"
- 'Cause you're gonna learn so fast.
- So, anyway, I think you have an idea.
- If you don't know the answer
- to any of the addition problems,
- that we give you in the exercises,
- you can press the "Hints," and it'll draw circles,
- and then 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!
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
|
Have something that's not a question about this content? |
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
abuse
- disrespectful or offensive
- an advertisement
not helpful
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
wrong category
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site
Share a tip
Suggest a fix
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.