>> This is from Math Gal,
Julie Harland.
Please visit my website
at yourmathgal.com or all
of my videos are organized
by topic.
A lot of people have trouble
subtracting using the usual
algorithm which is the method
where you go from right
to left with borrowing.
For instance let's say you
have 3204 minus 1869
so the way most people learn
to do this is they can't do 4
minus 9 so they borrow,
of course you can't borrow
from a 0 so they have to go
over here.
That makes 1
and they put the 1 here then
they borrow
that from the 10 make that a 9
and put a 1 here.
So this is the usual way
of doing it.
You have 14 minus 9 is 5
and then 9 minus 6 I can now
do a 3 but now I have this
problem of 1 minus 8
and I can't do that.
So I borrow again.
And then we have 11 minus 8 is
3 and t minus 1 is 1
and all right,
that should be the answer.
And then we could simply check
it by adding these 2 numbers
and get the original.
So that means I would take
1335 and add it to 1869
and there are many ways you
can add too.
You can add from left
to right, or right to left.
I'm going to do the
traditional one.
5 plus 9 is 14 carry the 1
and that gives you a 10 carry
the 1 12 carry the 1
and then we say was
that the original number
up here?
3204? Yes.
Okay, that's traditional.
Now let's do one that is going
from left to right instead.
Take the same problem.
3204 minus 1869.
All right.
So what do I mean,
going left to right?
Well, we'll just start
from the left
and we'll say 3 minus 2,
I'm sorry, 3 minus 1 is 2
and now here's a problem.
I have 2 minus 8.
All right.
Well, what I do is, instead,
I borrow from my answer.
So I'm going to borrow
from my answer
and put a 1 up here.
And now I'm going
to do 12 minus 8
and that will be 4.
And, okay, here's a problem.
0 minus 6.
Can't do that so I borrow
from my answer, subtract 1
and now I can do 10 minus 6
which is 4 and let's see.
4 minus 9, can't do that,
I'm going to borrow
from my answer,
so I can do 14 minus 9 is 5.
So these minus 1's you see
down here, you just subtract
so 2 minus 1 is 1335
and that's the way you can
subtract from left to right.
All right.
Let's try another one.
So I have 6312 minus 3519,
I know that's really 6,312
all right.
So 6 minus 3 is 3.
You can't do 3 minus 5
so I borrow like this
and then I do 13 minus 5 is 8.
Hm. 1 minus 1 I can do,
that's 0.
2 minus 9 I can't do
so I borrow
and then I can do the 12 minus
9 is 3.
Now look what happens here
when I subtract.
I have the 3 minus 1 is 2
but you have to think of this
as 80 minus 1.
So what will that be?
79 and then 3.
So let's go ahead
and check our answer.
I would check
by taking the answer I got
2793, adding it to the 3519
and I'm going to add
from left to right.
On another video I showed you
how to add going
from left to right.
2 and 3 is 5, 7 and 5 is 12,
I'm just going to write the 12
like this.
9 and 1 is 10, I'm just going
to write the 10 like this.
And then 3 and 9 is 12
and I have 6312
and that was the original
number up here.
So that means this is correct,
that is the right answer.
Now, some people don't
like writing these minus 1's
here, they want
to save a little space.
Let me show you another way
you can do this.
It's real similar.
You still do 6 minus 3 is 3
but when you do 3 minus 5 you
just borrow by just cancelling
out like that.
And what that means is you're
going to subtract 1 later.
So this will give you 13 minus
5 which is 8, 1 minus 1 is 0
and then I have, again,
I can't do 2 minus 9
so the trick here is you can't
really just take away from 0
so you would have to cross
out 80 to do 12 minus 9 is 3.
When you slash in front
of a number it means you just
subtract 1.
So, 1 less than 3 is 2,
1 less than 80 is 79
and this is still 3.
I actually like it better,
writing the minus 1, myself
but when I first learned it,
it was called slash arithmetic
where you could just slash it
out like that.
Okay. So that's all there is
to subtracting
from left to right.
This is one of many methods
of subtraction.
You could look
at my other subtraction
methods to see if you like it.
Of course if you already know
how to subtract with borrowing
and that's easy
for you then no problem,
you can continue to do
that for the rest
of your life.
What really matters is
that you can subtract
and get the right answer
and not be confused by it.
This is from Math Gal
Julie Harland.
Please visit my website
at YourMathGal.com where all
of my videos are organized
by topic. ------------------------------0da76481d838--