Use the commutative law of addition-- let me underline
that-- the commutative law of addition to write the
expression 5 plus 8 plus 5 in a different way and
then find the sum.
Now, this commutative law of addition sounds like a very
fancy thing, but all it means is if you're just adding a
bunch of numbers, it doesn't matter what order you add the
numbers in.
So we could add it as 5 plus 8 plus 5.
We could order it as 5 plus 5 plus 8.
We could order it 8 plus 5 plus 5.
These are all going to add up to the same things, and it
makes sense.
If I have 5 of something and then I add 8 more and then I
add 5 more, I'm going to get the same thing as if I had
took 5 of something, then added the 5, then added the 8.
You could try all of these out.
You'll get the same thing.
Now, they say in a different way, and then find the sum.
The easiest one to find the sum of-- actually, let's do
all of them.
But the easiest one, just because a lot of people
immediately know that 5 plus 5 is 10, is to maybe start with
the 5 plus 5.
So if you have 5 plus 5, that's 10, plus
8 is equal to 18.
Now, let's verify that these two are the same exact thing.
Up here, 5 plus 8 is 13.
13 plus 5 is also 18.
That is also 18.
If we go down here, 8 plus 5 is 13.
13 plus 5 is also equal to 18.
So no matter how you do it and no matter what order you do it
in-- and that's the commutative law of addition.
It sounds very fancy, but it just means that order doesn't
matter if you're adding a bunch of things.