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## 5th grade

# Creating a fraction through division

In this video, we'll learn about the relationship between division and multiplication using fractions. Watch how dividing by a number is the same as multiplying by its reciprocal. Then watch as Sal practices this concept using a fun, everyday example. Created by Sal Khan.

## Want to join the conversation?

- No matter how many times fractions are explained to me I can't get it to click in my head.

So when you are dividing a number by a number smaller than itself, does the product represent how many sections of the whole you have?

How does changing the division sign to a times sign, and flipping the fraction express the same thing?(39 votes)- I feel you I can never understand fractions as decimals.(7 votes)

- snickers up vote plz(19 votes)
- is the 3/4 equation always like that? Please explain.(11 votes)
- 3/4 really just means 3 divided by 4. Just like 1/4 means one divided by four. I like to use money as an example. If you have a one dollar bill and give it to your sister for "quarters" you get back four quarters. Another way to write that is 4/4 or four fourths of a dollar. If you reduce 4/4 to lowest terms by dividing the top and the bottom by four you get 1/1 which is just 1 - one dollar. Did that help?(14 votes)

- why is ur wife cutting bars or saops with a saw??! use a knife like, SHEESH!(16 votes)
- does the soap look like cheese cake or is it just me?(9 votes)
- i think it does or it might just look like some sorta dessert(10 votes)

- i dont even know how to do this and i watched this 2 times

please explain how to do this to me :((7 votes)- Ask your teacher(13 votes)

- can i get 10 votes ;)(12 votes)
- Why when you use a hint in Khan Academy they count it as an incorrect answer(10 votes)
- It’s because the last hint gives you the answer(4 votes)

- if you want to experience all of the smells then just sniff them.(11 votes)
- have you ever been beaten by a wet spaghetti noodle?(9 votes)
- I
**am**a wet spaghetti noodle.(4 votes)

## Video transcript

My wife and I have recently
purchased an assortment pack of soap, and we both want
to experience all 3 bars. And we are not willing to
share soap with each other. So we have a little
bit of a conundrum. How do we share
these 3 bars of soap so that we each get to
experience all of the smells? So this might be
a nice rose smell. This might be some
type of ivory smell. I don't even know if
that's a legitimate smell. This might be some
type of sandalwood, which is always very nice. And my wife has an idea. She says, look I'm going
to take these 3 bars, so we're starting
with 3 bars of soap. And I'm going to divide
it into 2 equal groups. And I said, how are
you going to do that? And she says, well, I'm
just going to take out some type of carving
saw or carving knife, or who knows what
it is, and I'm just going to cut it right down the
middle, so right down this. This is my wife cutting the soap
right over here with her saw. So she's cutting the
soap right over here. So she has divided the
soap into 2 equal groups. So she's taken 3 bars, and she's
divided into 2 equal groups. So the interesting question
here is, how many bars of soap do we each have now? And I encourage you
to pause the video and think about
that for a second. How many bars of soap
do we each have now? Well, let's just
visualize my share. Let's say I take this
bottom half right over here. So this is Sal's
share of the soap. Let me write this out. So this is Sal's share. My wife took this top half. Well, what do I have? Well, I have 1/2, I have another
1/2, and I have another 1/2 of a bar. So I have 3/2 bars of soap. Or you could say that I have
3 times 1/2 bars of soap. Notice, something very
interesting happened here. 3 divided by 2 is
equal to 3 times 1/2. And we could make it
even more interesting, because we know 2 is the
exact same thing as 2/1. So 3 divided by 2/1 is
equal to 3 times 1/2. Notice we went from a
division to a multiplication, and we took the reciprocal. And that makes complete sense. We have 3/2 bars now. But what's 3 times 1/2? Well, 3 times 1/2
is equal to 3/2. So just doing this little
simple, smelly soap example, we've got a very
interesting result. 3 divided by 2 is the
same thing as 3 times 1/2, which is the same thing as 3/2.