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## Class 7 (Foundation)

### Unit 2: Lesson 2

Properties of whole numbers# Commutative law of multiplication

Commutative Law of Multiplication. Created by Sal Khan and Monterey Institute for Technology and Education.

## Want to join the conversation?

- I notice you use a circle for the multiplication sign at0:35, does that signify a difference in the problem?(6 votes)
- Captain, once you get deeper into maths and working with variables then we have to use the dot or else it will get confused with the variable X(2 votes)

- ok, why did you multiply 34*2 like this 2

* 34

-----------

8

+ 60

------------

68

when you could have just done this

2 2 * 4 = 8

* 34 2 * 3 = 6

--------- and your done

68(3 votes)- He's using Long Addition and Long Multiplication i'm seeing a lack of explaining some things in the videos that i think Sal needs to do to help us make Connections between things better.

I JUST left a comment to on the Commutative law of addition video about this because i saw it coming lol. There's also Long Subtraction and Long Division which is like the Carrying Numbers method writing the numbers under each other, do a Google search on it you'll see what i mean. It still comes back to which method you prefer though taking Notes on Concepts you need to choose a particular method is super helpful to help you organize your thoughts and work.(2 votes)

- hey is this kidnergarden?(3 votes)
- 5x + 4; commutative law for multiplication(3 votes)
- 5x + 4 = x * 5 + 4. It is usually the convention to write it as 5x instead as it's shorter.(1 vote)

- 0.54 why does the number that is the least go on the top(1 vote)
- The purpose of this video is to show you that the commutative property allows you to multiply the numbers in any order. The smaller number can go on top as Sal did in his 1st version or you can put the larger number on top. It doesn't matter. Both versions create the same answer!(3 votes)

- So it doesn't matter which order it's in?(1 vote)
- No, it doesn't matter. If you multiply 3*2 and 2*3, you will still get 6 either way.(2 votes)

- why is associative different than communicative(1 vote)
- They tell you that you can do different things.

The commutative property tells you that you can change the order of the numbers when you are multiplying and you will get the same result: 2*3 = 3*2

The associative property tells you that you are allowed to move the grouping symbols for multiplication and you will still get the same result: 2 * (3 * 4) creates the same answer as (2 * 3) * 4

Hope this helps.(2 votes)

- is commutative law of multiplication usefull in our life(1 vote)
- would this be commutative or associative?

2x(15+2)

(15+2)x2

Thanks(1 vote) - At1:17, at the question, what if there was no commutative law of multiplication?(1 vote)
- Then it would be way too different to calculate.(1 vote)

## Video transcript

Use the commutative law of
multiplication to write 2 times 34 in a different way. Simplify both expressions
to show that they have identical results. So once again, this commutative
law just means that order doesn't matter. It sounds very fancy. Commutative law of
multiplication. But all that says is that it
doesn't matter whether we do 2 times 34 or whether
we do 34 times 2. The order does not matter. We can commute the two terms.
Both of these are going to get you the same exact answer. So let's try it out. What is 2 times 34? And we could write it like
this, literally. You'll almost never see it
written like this, but it is literally 2 times 34. Almost always people write the
larger digit on top, or the digit with more digits,
or the number with more digits on top. But let's do it this way. 4 times 2 is 8, and then
we'll put a 0. 3 times 2 is 6, or you can view
it as 30 times 2 is 60. Add them together. 8 plus 0 is 8. 6, bring it down. It's not being added
to anything. You get 68. So 2 times 34 is 68. Now, if you do 34 times 2, 2
times 4 is 8, 2 times 3 is 6. That's why it's always nicer to
write the number with more digits on top. It also is equal to 68. So it doesn't matter whether you
have two groups of 34 or thirty-four groups of 2,
in either case, you're going to have 68.