# Basic subtraction | Addition and subtraction | Arithmetic | Khan Academy

Welcome to the video
on basic subtraction. Let’s do a little bit a review
of basic addition first. If I said 4 plus 3,
what did this mean? What did that equal? Well, there were a couple of
ways we could have viewed this. We could have said I
or I don’t know, I had 4 lemons for breakfast. So 1, 2, 3, 4 lemons
for breakfast. And let’s say, I had another
3 lemons for lunch. 1, 2, 3, and so you could
view 4 plus 3 as how many total lemons did I have? I’m adding 3 to 4. So how many total did I have? Well, it’s 1, 2, 3, 4, 5, 6, 7. So I had a total of 7 lemons. Another way we could have
viewed that is we could have drawn our number line. And I’ll draw it in yellow
because– now that’s not wide enough. I’ll draw it in yellow because
we’re talking about lemons. So let’s say that’s
our number line. And if I start at the number–
let me draw all of the numbers. 0, 1, 2, 3, 4, 5, 6, 7. So you could think about
this as saying, well, we’re on the number line. We start at the number 4. That’s this number 4. And we’re adding 3 to it. So we’ll increase, along
the number line by 3. So we’ll go 1, 2, 3
and you end up at 7. So you could say if I have 4
and I get 3 more, I get 7. Or if I increase 4
by 3 I also get 7. So what’s subtraction now? Because that’s what
this video is about. I shouldn’t waste all of our
example of 4 minus 3. What is that equal to? Let me switch colors just to
keep things interesting. So what is 4 minus 3 equal to? Subtraction or minus is
something more, you’re adding. I don’t want to use the word
then I had 3 more. In subtraction
you’re taking away. So this example, if I started
with 4 lemons, let’s say I had 4 lemons on a plate. If I’m subtracting 3, if I’m
I’m going to take 3 away. So maybe I’m eating them
or maybe I’m giving them to you in exchange for
watching these videos. So to take away 3 from this 4,
let’s say this one goes away, this one goes away, and
this one goes away. How many lemons
would we have left? Well, this is the only one
that I haven’t crossed out. So we would have 1 lemon left. And this would be the
lemon that’s left. Didn’t have to be that
one, I could have crossed out any of the 3. Another way to view that,
let’s draw the same lemon colored number line. Let’s say that this is the
number line right here. And I’ll draw all
the same numbers. So that’s 0, 1, 2,
3, 4, 5, 6, 7. Of course, the number
line keeps going. There’s no largest number. And you can imagine, any number
that you can think of, I can think of one higher than that. So there is no largest number. So that’s why we draw
that arrow there. I could never draw the
entire number line. But anyway, back
to subtraction. So we’re starting at
4 lemons, right? When we added 3– plus 3– we
went to the right 4 spaces on the number line. And that’s because the
right is increasing value. So we went from 4 to 5. That was one more. 5 to 6 was two more,
and 7 was 3 more. Now we’re taking away from 4. So what do we do? What would you think we do? Well, since we’re taking away
we’re going to decrease the total number of lemons we have. So we take away
one, we get to 3. Take away two, get to 2. Take away three, we took
away three, right? So we’ll go back 1, 2, 3
along the number line and we’ll end up at 1. And that’s this 1 right here. So just to review, addition is
you’re doing more or something. Subtraction is you
are taking away. If you think about it on the
number line, addition is increasing along the number
line by that amount. So in this case we increased
along the number line by 3. And so we went from 4 to 7. In the subtraction case
we decrease back on the number line. So we decrease by the amount
that you’re subtracting. So in this case we
decreased by 3. We went back 1, 2,
3 and we had 1. And the other way to view it,
if I have 4 of something. If I give 3 away or if I ate
3 of them or I don’t know what I did to 3 of them. If I lost 3 of them I
would have 1 left. Now let me show you some
interesting things about subtraction. So we know that 4 minus
3 is equal to 1. Let me show you something
else that’s interesting. What is 4 minus 1? Well, we could use
either example. Let’s do the lemon example. Let’s do apples now; I’m
bored of the lemons. Let’s say I 1, 2, 3, 4. I have a new pen, sometimes
it doesn’t draw right. Let’s say I had 4 apples. This is the example
we’re dealing with. And I were to eat one of them. So one of them were to go away. How many apples
would I have left? Well, 3– 1, 2, 3. So 4 minus 1 is equal to 3. And if we did it on the number
line, if we started at 4 and we subtracted 1– we took 1 away. So we’re going to
become one smaller. We go back one, we get 3. Either way works. But isn’t this interesting? 4 minus 3 is equal to 1 and
4 minus 1 is equal to 3. You might say, well, did I pick
the numbers just so it worked? Well, it turns out that
it’s always true. Well, I don’t want to get too
technical, but we’re already touching on something that
you’ll learn later, maybe in algebra one day. But actually I don’t want to
go into all that right now. So where does this come from? Well, this is also based on
the fact that 3 plus 1– I didn’t want to confuse you. So I apologize if I did. But I’ll show you another
interesting thing. What is 3 plus 1? 3 plus 1 is equal to what? Well, that’s easy. You know that from
basic addition. You can start on the number
line at 3 and add 1 do it. And where do you end up? You end up at 4. 3 plus 1 is equal to 4. Or you could have started at 1
on the number line and added 3. 1, 2, 3 and you would
have also ended up at 4. So we also know that you could
have switch this either way. Both of those are equal 4. What do you see here? Well, there’s a bunch of things
I’ve written here and they all kind of relate to each other. 1 plus 3 is equal to 4. 3 plus 1 is equal to 4. 4 minus 1 is 3. Essentially, 4 minus 1 and
getting 3 is the exact same– you’re saying the same thing
as 3 plus 1 is equal to 4. This statement says if
I add 1 to 3 I get 4. This is saying if I take
away 1 from 4 I get 3. So if I start at 4,
move back, I get 3. This is saying if I start at
3, and I move up 1, I get 4. Hopefully that gives you a
little bit of intuition about what subtraction is. In the next video I’ll just do
as many basic subtraction problems I can do
in 10 minutes. And then you’ll be ready
to do the exercises. See you soon.

## 41 thoughts on “Basic subtraction | Addition and subtraction | Arithmetic | Khan Academy”

1. pandaBee says:

ur BORED of the lemons? Lol wow

2. Cambodia69 says:

@Admail233 You might want to add the U.S. where many children also don't have access to decent education. And having what you propose in Africa, though a great idea, would be dangerous to those nations who profit from stealing Africa's natural resources. Not only are there political and corporate obstacles to your idea but religious ones as well. There's nothing more dangerous than a well informed citizenry. That said, are you familiar with OLPC? I gave to them in 2009 – back when I had money.

3. Airclot says:

@LordAlda I fapped to this comment.

4. axexaera says:

@Shadyhunter04 Im 17 And I watch this videom because I need some help with math! Got a problem?

5. taylor9610 says:

i don,t like lemons

6. MrZEALOT98 says:

@lizardgizzard108 no i do to!!

7. Julian Abio says:

Excellent videos. If there's one positive piece of criticism I can give you. I know what part of the board you are talking about but the average child would have a hard time following it.
Solution: make the pen tip much more visible.
Thanks.

8. MrElectropolis says:

Ahhh I still don't get it!

9. Jake Thayer says:

I don't eather

10. Vellzi says:

Who has four lemons for breakfast?!

11. Al Khalil says:

your way is fantastic. thank you very much

12. Shinji Ikari says:

I still don't get it.

13. toddkw says:

>lemons for breakfast and lunch

14. kochmannrobert799 says:

If I ever have kids, this is what they are going to watch.

Gonna use some of your vids homeschooling next year!!

16. chasitytheepic says:

hey im wearing a bra whats up niggas

17. Jacob C says:

This shit is so hard to understand!!

18. R Ree says:

Sorry, cab someone please explain to me the end from the 3 plus 1 part.

19. R Ree says:

Sorry, how does information at the end go into Algebra?

20. CQN APDN says:

21. CQN APDN says:

Do you want us to explain what is algebra?

22. R Ree says:

He says we'll see that in A;egabra and I am wondering, ho wdo we see it in Algebra?

23. AR78gaming says:

1 number

24. Imani McBean says:

I love that Video. Also

25. Combination Card Game, LLC says:

Thanks for the video! For another fun way to learn basic math, check out the exciting new card game, Combination!

26. Ore Creeper says:

The lemons were a bad idea, I would never eat any plain

27. Ore Creeper says:

The youtuber Crainer Commentates said SSundee is so good at trolling in CrundeeCraft he gave up

28. Ore Creeper says:

Crainer fans u shouldn't be his fans anymore

29. Ore Creeper says:

#perfectexplanation

30. Meiruki says:

Who the heck eats lemons for their meals

31. William Rezaee says:

my goodness these are like the first Khan Akedemy videos

32. Bacon Hair Mania says:

zzzzzzzzzz,huh?

33. Bacon Hair Mania says:

34. 2kshootingreens Bruh says:

crickets in background

35. Megan Cericola says:

Three Rivers school

36. Jalaluddin Kazi says:

Write the degree of the following polynomial. ab2cd – 3a2bcd3 +2ac4.

37. kalim pathan says:

Im software engineer and im watching this video.. wanted to clear some doubts.. :-D.. nicely explain..

38. Kairy Barazi, M.D. says: