Hello guys, today we are playing with some
toys from my bathtub.
We are going to learn about a few things today
that are really cool in addition and subtraction.
We will use some of my toys to help us.
Let’s take a look.
Here are some ducks.
We have 3 blue ducks and 7 yellow ducks.
Can you tell me how many ducks we have in
all?
We have 10 ducks all together.
When you add 3 and 7 you get 10 ducks in all.
Now here is something really cool.
The ducks just moved position.
Is the answer still the same?
Yes, the answer is still 10, the same as before.
In addition we have what we call the commutative
property.
This seems like something difficult to understand
but it is not.
All it means is that when we are adding numbers
together they can be switched around as much
as you want and the answer will still be the
same.
This only works for addition so remember that.
Here is a math problem where we can use what
we just learned.
It says if 8 plus 2 equals 10, then blank
plus 8 equals 10.
We need to fill in the blank with the missing
number.
We know that 8 plus 2 equals 10.
We just learned that in addition we can switch
the 8 and 2 around and still get the same
answer of 10.
So to fill in the missing number what do you
think it will be?
The missing number is 2.
The numbers 8 and 2 were just switched.
With the 2 in the blank we get 2 plus 8 equals
10 and that is true.
Great job kids.
Here is another math problem but this time
it is subtraction.
The problem says “ If 9 subtract 4 equals
5, then 9 subtract 5 equals blank”.
We need to fill in the blank.
The first thing we should know is that subtraction
is not the same as addition.
In addition we can switch the numbers around
but not with subtraction.
But addition and subtraction are similar in
some ways.
Let me show you what I mean.
Here is a math mountain.
If you are not familiar with a math mountain
that is just fine.
At the top we have the total.
At the bottom we have what we call partners
or addends.
The total is 9 and the partners are 4 and
5.
We can use both subtraction and addition with
this math mountain.
If we add the 4 and 5 together we get the
total of 9.
We can also subtract.
Just like the first part of the problem below,
9 subtract 4 equals 5.
Let's solve the part of the problem we don’t
know.
9 subtract 5 equals what?
You probably figured it out but let’s use
addition to find the answer.
We will start at the partner we know which
is 5.
Let’s count up from 5 until we get to the
total.
Starting from 5 we count 6….7…….8…...9
We counted 4 numbers so the other partner
is 4 Amazing job.
I’m sure you can now see that subtraction
and addition are related.
I want to show you one last addition skill.
The problem says 2 plus 6 plus 4 equals 12
is the same as 10 plus blank equals 12.
When we are doing addition with more than
two numbers like this it is helpful to make
groups of doubles or tens.
In this example we can combine the 6 and the
4 together to make 10.
Adding with ten is much easier than trying
to add 2 plus 6 plus 4.
Many of you already know partners of 10 like
6 and 4, 5 and 5, 3 and 7, and so on.
Now we just have to add 2 plus 10 which is
12.
It saves us time to combine numbers that make
10 and then add the other numbers.
So the blank in this problem should be filled
with what number?
The answer is 2.
Ten plus 2 equals 12.
Great job again.
That was a long lesson but it will help you
as you add and subtract.
Thanks for coming, we will see you next time.
