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## 6th grade (Illustrative Mathematics)

### Unit 6: Lesson 9

Lesson 9: The distributive property, part 1# Distributive property over addition

CCSS.Math:

Learn how to apply the distributive law of multiplication over addition and why it works. This is sometimes just called the distributive law or the distributive property. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- one question i had when he said 4times(8+3) but the equation is actually like 4(8+3) and i don't get how are you supposed to know if there's a times table there.its on 19-39 on video.(13 votes)
- If there is no space between two different quantities, it is our convention that those quantities are multiplied together. Doing this will make it easier to visualize algebra, as you start separating expressions into terms unconsciously.

4 (8 + 3) is the same as (8 + 3) * 4, which is 44.(2 votes)

- i need help to this problem 2(5-v)(10 votes)
- you confusing me with this?(10 votes)
- why is the distributive property important in math? how can it help you? isn't just doing 4x(8+3) easier than breaking it up and do 4x8+4x3?(8 votes)
- When you get to variables, you will have 4(x+3), and since you cannot combine them, you get 4x+12. So you are learning it now to use in higher math later.(1 vote)

- i need the anser to this problem 7(-9r-5) pls help(4 votes)
- i dont understand how it works but i can do it(4 votes)
- Ok so what this section is trying to say is this equation 4(2+4r) is the same as this equation 8+16r. The reason why they are the same is because in the parentheses you add them together right? That would make a total of those two numbers. Those two numbers are then multiplied by the number outside the parentheses. So in doing so it would mean the same if you would multiply them all by the same number first. You would get the same answer, and it would be helpful for different occasions! This is a choppy reply that barely makes sense so you can always make a simpler and better explanation. Hope this helps!(2 votes)

- this is frustrateing(4 votes)
- I"m a master at algeba right?(3 votes)
- i don't know, if sal says that it probably means you can be one too!(2 votes)

- I remember using this in Algebra but why were we forced to use this law to calculate instead of using the traditional way of solving whats in the parentheses first, since both ways gives the same answer.(1 vote)
- It is useful in algebra(4 votes)

- How is it possible to distribute first then do the parentheses ? Order of operations Says parentheses first?(1 vote)
- The distributive property is an acceptable way of eliminating parentheses provided the parentheses contain only addition/subtraction, and you have a value to be multiplied with the parentheses. In that situation, there is no conflict/violation of the order of operations rules. You are eliminating the parenthese by doing the distribution.(5 votes)

## Video transcript

Rewrite the expression 4 times,
and then in parentheses we have 8 plus 3, using the
distributive law of multiplication over addition. Then simplify the expression. So let's just try to solve
this or evaluate this expression, then we'll talk
a little bit about the distributive law of
multiplication over addition, usually just called the
distributive law. So we have 4 times
8 plus 8 plus 3. Now there's two ways to do it. Normally, when you have
parentheses, your inclination is, well, let me just evaluate
what's in the parentheses first and then worry about
what's outside of the parentheses, and we can do
that fairly easily here. We can evaluate what
8 plus 3 is. 8 plus 3 is 11. So if we do that-- let me do
that in this direction. So if we do that, we get 4
times, and in parentheses we have an 11. 8 plus 3 is 11, and then this
is going to be equal to-- well, 4 times 11 is just
44, so you can evaluate it that way. But they want us to use the
distributive law of multiplication. We did not use the distributive
law just now. We just evaluated
the expression. We used the parentheses first,
then multiplied by 4. In the distributive law, we
multiply by 4 first. And it's called the distributive law
because you distribute the 4, and we're going to think
about what that means. So in the distributive law, what
this will become, it'll become 4 times 8 plus 4 times
3, and we're going to think about why that is in a second. So this is going to be equal to
4 times 8 plus 4 times 3. A lot of people's first instinct
is just to multiply the 4 times the 8, but no! You have to distribute the 4. You have to multiply it times
the 8 and times the 3. This is right here. This is the distributive
property in action right here. Distributive property
in action. And then when you evaluate it--
and I'm going to show you in kind of a visual way
why this works. But then when you evaluate it,
4 times 8-- I'll do this in a different color-- 4 times 8 is
32, and then so we have 32 plus 4 times 3. 4 times 3 is 12 and 32 plus
12 is equal to 44. That is also equal to 44, so
you can get it either way. But when they want us to use
the distributive law, you'd distribute the 4 first.
Now let's think about why that happens. Let's visualize just
what 8 plus 3 is. Let me draw eight
of something. So one, two, three,
four, five, six, seven, eight, right? And then we're going to add to
that three of something, of maybe the same thing. One, two, three. So you can imagine this is what
we have inside of the parentheses. We have 8 circles
plus 3 circles. Now, when we're multiplying this
whole thing, this whole thing times 4, what
does that mean? Well, that means we're just
going to add this to itself four times. Let me do that with
a copy and paste. Copy and paste. Let me copy and then
let me paste. There you go. That's two. That's one, two, three, and then
we have four, and we're going to add them
all together. So this is literally what? Four times, right? Let me go back to the
drawing tool. We have it one, two, three, four
times this expression, which is 8 plus 3. Now, what is this
thing over here? If you were to count all of this
stuff, you would get 44. But what is this thing
over here? Well, that's 8 added to
itself four times. You could imagine you're
adding all of these. So what's 8 added to
itself four times? That is 4 times 8. So this is 4 times 8,
and what is this over here in the orange? We have one, two, three,
four times. Well, each time we have three. So it's 4 times this
right here. This right here is 4 times 3. So you see why the distributive
property works. If you do 4 times 8 plus 3, you
have to multiply-- when you, I guess you could imagine,
duplicate the thing four times, both the 8 and the
3 is getting duplicated four times or it's being added to
itself four times, and that's why we distribute the 4.