Hi everyone in this video
i'm going to show you how to subtract
decimal numbers
so there are two basic rules of
subtracting decimal numbers
the first rule is to line up the decimal
points of the decimal numbers
and the second rule is to subtract
digits in the same place value position
If you need a quick review of place
value please check my adding decimal
numbers video
I will be going over these problems
throughout the video
and I will also have quick review of
subtracting whole numbers so you get the
idea of how to subtract decimal numbers
so the first problem is to subtract
5.774
by 2.371 so we're going to follow the
first rule by lining up the decimal
points of the two numbers
And you can write a subtraction sign in the front
and then we are going to subtract from
right to
left so the second rule says to subtract
digits in the same place value position
so let's look at the thousandths place
first
four minus one is three
and then at the hundredths place seven
minus seven
is zero at the tenths place
seven minus three is four and we just
copy down the decimal points that we
line up
and at the ones place five minus two is
three
so the answer of this problem is 3.403
now before we go over the next problem I
want to have a quick
review of subtracting whole numbers
Let's say we want to
subtract 9 from 31
and what you want to do is first you
write down 31 and then you write
9 at the ones place because
it's only one digit and we don't have
enough to subtract from one because we
have a nine
so we need to borrow a one from three
and if we borrow one from three we have
two left
and i'm going to show you what it means
on the right side so
if you have 30 when you borrow a 1 that
means you borrow
10 so you have 20 left
and now that we borrow a 10 10 plus 1
is 11 so that means we will have 11 here
and we need to subtract 11 sorry we need
to subtract 9 from 11
so 11 minus 9 is 2
and because we have the 20 left we write
it down
at the tens place so our final answer is
22
and we're going to use the same logic
when we borrow
numbers later in the following problems
so our next problem is 6.68 minus 4.78
again follow the first rule we're going
to line up the decimal points
and we're going to subtract from right
to left
so on the right side at the one
hundredths place
eight minus eight is zero so just write
down zero
and at the tenths place we have six
minus seven
and we don't have enough so we need to
borrow
a one from the ones place and if you
look at the top
we have six right here and when after we
borrow a one
we have five left so then we can
cross out this 6 and make it 16 because
we already borrow one from the other
side
16 minus 7 is 9
and then we just write down the decimal
point and since we have the
5 left 5 minus 4 gives us one
so our final answer is one point nine
next problem we have six point six minus
four point seven
eight i already line up the decimal
points
but notice there's space above eight you
can just write a zero here
and now if you look at this we see that
we don't have
enough to subtract eight so we need to
borrow a one
from the tens place
so after you borrow a one you will have
five left so let's cross out and write five
and then we can cross out the zero and
write ten
so ten minus eight is two and if you
look at the tenths place
you see that five minus seven we don't
have enough to
subtract again so we're going to borrow
from the ones place
so cross out the six and we write
five
because you're only borrowed one so
now we need to make the number
on the tenths place 15 so 15
minus seven is eight and we copy down
the decimal point
all right so look at the ones place five
minus four equals one
so our final answer is 1.82
all right the next problem you need to
subtract four point
seven eight from six notice
when i write the two numbers vertically
you don't see the decimal point for six
but how do i know i need to put six
right there
if you think about this 6 is basically
6.00 and these two numbers are
equivalent
and you always have a decimal point
to the right of the ones place
and to the left of the tenths place
all right so that means i just need to
write the decimal point here and write
the zero
zero but before we go over this problem
I want to do a quick review of
subtracting whole numbers because it
will really help you to understand what
we are going to do next
so let's say i'm subtracting 100
by 78.
now if you look at this you know that we
don't have
enough to subtract 8 because it's only
zero there's nothing we can do
but then there's also nothing to borrow
from the place to the left because it's
another zero
so what you're going to do is you just
have to borrow from
the next next number place over
all right think of it as you're
borrowing
1 from a 10. so after you borrow a 1
from a 10 you're going to get a 9
right so if you already borrow a 1
then you can write 10 here so 10 minus
8 is 2 and then you have 9 minus
7 which is 2 and when you subtract
100 by 78
you do get 22. so we're going to use the
same logic for
the problem on the left side
now in this problem we don't have enough
to
subtract 8 we also don't have enough to
subtract 7 so what i'm going to do is
i'm going to borrow
a one from let's think of this as 60
right so that means i will have 59 left
so i'm going to write
five above the six and nine above the
zero on the tenths place
so since i borrow a one i can cross out
this 0 and then
write 10. 10 minus 8 is 2.
and if you look at the tenths place 9
minus 7
gives you 2 and then
on the ones place you have 5 minus 4
which is 1 and
also don't forget to copy down the
decimal point
so the answer of this problem is 1.22
in the last problem we're going to
subtract 3.008 from 6.002
so now we have another zero but it's
okay we're just gonna use
the same method again notice you don't
have enough
to subtract eight from two so we're
going to
borrow from the next place over but now
we have two
zeros so what we're going to do is we
are going to think of this
as we're borrowing 1 from 600
so we know that 600 minus 1 equals 599
right so we can just cross out this and
write
5 on top of 6 and then
nine on top of zero and another nine on
top zero
and now that we borrow a one we are
going to
change the two to twelve so
twelve minus eight is four
and if we look at the hundredths place
nine minus zero is just nine so we write
it down and
simple for tenths place nine minus zero is
nine again
and we copy down the decimal point and
on the ones place
five minus three is two so finally our
answer for this
problem is two point nine
nine four
