Main content

### Course: Get ready for 6th grade > Unit 4

Lesson 3: Associative property of multiplication# Properties of multiplication

Sal uses pictures and practice problems to see commutativity and associativity in multiplication. Created by Sal Khan.

## Want to join the conversation?

- What is PEMDAS?(143 votes)
- This is called the order of operations, which we call PEMDAS because there is a reason behind it.

P (Parentheses)

E (Exponents)

M (Multiplication)

D (Division)

A (Addition)

S (Subtraction)

Or as my teacher calls it- Please Excuse My Dear Aunt Sally, which also contains the same abbreviation- I don't get it.

But there is an example for this.

Let's say you have this problem on your test ( or whatever )

(64*3)+ ( 54 divided by 4 )- 13=x

Post your answer in the comments below and leave a like! Hopefully you found this helpful!(35 votes)

- what property is 4(x+3)=(x+3)4(9 votes)
- That would be the commutative property of multiplication because 4 and (x+3) are switched.(15 votes)

- Hi in multiplication how would you calculate three digit numbers? Example 124 multiplied by 675= what?(5 votes)
- An interesting method is the Vedic (Indian) multiplication method called vertical and crosswise, which is not usually taught in U.S. schools.

Step 1: Multiply first digits: 1x6 = 6. This represents 6 ten-thousands so far.

Step 2: Cross multiply the first two digits by the first two digits, and add the products: (1x7)+(2x6) = 7+12 = 19. This represents 19 thousands. Adding this to 6 ten-thousands (or 60 thousands) gives a total of 79 thousands so far.

Step 3: Cross multiply the three digits by the three digits, and add the products: (1x5)+(2x7)+(4x6) = 5+14+24 = 43. This represents 43 hundreds. Adding this to 79 thousands (or 790 hundreds) gives a total of 833 hundreds so far.

Step 4: Cross multiply the last two digits by the last two digits, and add the products: (2x5)+(4x7) = 10+28 = 38. This represents 38 tens. Adding this to 833 hundreds (or 8,330 tens) gives a total of 8,368 tens so far.

Step 5: Multiply last digits: 4x5 = 20. This represents 20 units. Adding this to 8,368 tens (or 83,680 units) gives a final answer of**83,700**.

Have a blessed, wonderful day!(22 votes)

- [Solved]At1:37do you have to put the second numbers in brackets?(8 votes)
- No, the brackets just tell you what order to operations in. With multiplication, you can do it in any order

(2x3) x4 and (3x4)x2 are going to mean the same thing.(14 votes)

- ya what is a PEMDAS?(7 votes)
- PEMDAS stands for order of operations. This should really be written as P E MD AS.

P means parentheses. Calculate expressions in parentheses first.

E means exponents (powers). Do exponents next.

MD means multiplication and division. Do multiplications and divisions next, in order from left to right.**Note**: MD does**not**mean that multiplication must be done before division.

AS means addition and subtraction. Do additions and subtractions last, in order from left to right.**Note**: AS does**not**mean that addition must be done before subtraction.

Have a good day!(8 votes)

- If I had an equation like this (6+3)x9 could I switch the 9 to the front of the equation like this 9x(6+3)(5 votes)
- Yes, you will get the same answer either way.(11 votes)

- How did he know 8 divided by 3 was a fraction of 8 over 3?(5 votes)
- 8 over 3 is a different way to divide(8 votes)

- why are there letters in math(5 votes)
- Hi lb15009! The letters in math are called variables. Variables symbolize unknowns. Let's say you had x+2=3. The variable would be "x". Basically, variables are unknown numbers that are used in algebra and other equations. Hope this helps. Have an amazing day! 😆(7 votes)

- Why is it called the commutative property?(6 votes)
- The word "commutative" comes from "commute" which means to move around. In multiplication, the commutative property says you can move the numbers around and it is still the same answer. So, it's called commutative property because you can move the numbers around, hence "commutative."(4 votes)

- Do you need the parenthesis to solve the problems?(4 votes)
- ( )- these are parentheses

parentheses are used in math to define which part of a problem should be done first in order to get the desired answer.

for example: 5+(3*6)=?

Since the parentheses are around 3*6, then that means that you have to multiply 3*6 first and then add 5 to the product of 3*6, or 18.

So basically, you would solve it like this-

5+(3*6)=?

5+18=?

5+18=23

And so the answer is 23.(6 votes)

## Video transcript

So if you look at each
of these 4 by 6 grids, it's pretty clear that there's
24 of these green circle things in each of them. But what I want to show
you is that you can get 24 as the product of three numbers
in multiple different ways. And it actually doesn't matter
which products you take first or what order you
actually do them in. So let's think about this first. So the way that
I've colored it in, I have these three groups of 4. If you look at the
blue highlighting, this is one group of 4, two
groups of 4, three groups of 4. Actually, let me make
it a little bit clearer. One group of 4, two groups
of 4, and three groups of 4. So these three columns you
could view as 3 times 4. Now, we have another 3
times 4 right over here. This is also 3 times 4. We have one group of
4, two groups of 4, and three groups of 4. So you could view these
combined as 2 times 3 times 4. We have one 3 times 4. And then we have
another 3 times 4. So the whole thing we could
view as-- let me give myself some more space-- as 2 times--
let me do that in blue-- 2 times 3 times 4. That's the total
number of balls here. And you could see it based
on how it was colored. And of course, if you did 3
times 4 first, you get 12. And then you multiply
that times 2, you get 24, which is the total
number of these green circle things. And I encourage you now to
look at these other two. Pause the video and
think about what these would be the
product of, first looking at the
blue grouping, then looking at the purple
grouping in the same way that we did right over here, and
verify that the product still equals 24. Well, I assume that
you've paused the video. So you see here in this first, I
guess you could call it a zone, we have two groups of 4. So this is 2 times
4 right over here. We have one group of
4, another group of 4. That's 2 times 4. We have one group of
4, another group of 4. So this is also 2 times 4 if
we look in this purple zone. One group of 4,
another group of 4. So this is also 2 times 4. So we have three 2 times 4's. So if we look at each of
these, or all together, this is 3 times 2 times
4, so 3 times 2 times 4. Notice I did a different order. And here I did 3 times 4 first. Here I'm doing 2 times 4 first. But just like before,
2 times 4 is 8. 8 times 3 is still equal
to 24, as it needs to, because we have exactly 24
of these green circle things. Once again, pause the video
and try to do the same here. Look at the groupings
in blue, then look at the groupings
in purple, and try to express these 24 as some
kind of product of 2, 3, and 4. Well, you see first we
have these groupings of 3. So we have one grouping
of 3 in this purple zone, two groupings of 3
in this purple zone. So you could do
that as 2 times 3. And we have one 3 and another 3. So in this purple zone,
this is another 2 times 3. We have another 2 times 3. Whoops. I wrote 2 times 2. 2 times 3. We have another 2 times 3. And then finally, we
have a fourth 2 times 3. So how many 2 times
3's do we have here? Well, we have one, two,
three, four 2 times 3's. So this whole thing could be
written as 4 times 2 times 3. Now, what's this
going to be equal to? Well, it needs to
be equal to 24. And we can verify 2 times 3
is 6 times 4 is, indeed, 24. So the whole idea of what
I'm trying to show here is that the order in which
you multiply does not matter. Let me make this very clear. Let me pick a different example,
a completely new example. So let's say that I
have 4 times 5 times 6. You can do this multiplication
in multiple ways. You could do 4 times 5 first. Or you could do 4
times 5 times 6 first. And you can verify that. I encourage you
to pause the video and verify that these two
things are equivalent. And this is actually called
the associative property. It doesn't matter how you
associate these things, which of these that you do first. Also, order does not matter. And we've seen that
multiple times. Whether you do this or
you do 5 times 4 times 6-- notice I swapped the 5
and 4-- this doesn't matter. Or whether you do this
or 6 times 5 times 4, it doesn't matter. Here I swapped the
6 and the 5 times 4. All of these are going to
get the exact same value. And I encourage you
to pause the video. So when we're talking
about which one we do first, whether we do the 4
times 5 first or the 5 times 6, that's called the
associative property. It's kind of fancy word for
a reasonably simple thing. And when we're saying
that order doesn't matter, when it doesn't matter whether
we do 4 times 5 or 5 times 4, that's called the
commutative property. And once again, fancy word
for a very simple thing. It's just saying it doesn't
matter what order I do it in.