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welcome to math with mr j
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in this video i'm going to cover how to
calculate a discount by hand so we are
going to write everything out without
using a calculator this will show all of
the steps for calculating a discount and
then the final sale price based on that
discount let's jump into our example
where we have 35 percent off of 78.30
now the first thing that we need to do
is to calculate the discount so how much
money will be taken off the original
price we do this by multiplying the
original price
by the rate of discount the rate of
discount is in the form of a percent so
we need to convert that percent to
decimal form percent means per 100 so we
divide our percent by 100 to convert it
to a decimal we can do this by simply
moving the decimal twice to the left so
for our example let's move the decimal
twice to the left to change it to
decimal form so i'm going to rewrite 35
percent
underneath here so i have enough room
now 35 percent that's a whole number so
our decimal comes at the end of a whole
number we typically don't write it in
there because we do not need it with it
being a whole number let's move it twice
to the left
once
twice
so it's going to come before the three
so we have
0.35 that's our decimal form of 35
so once we have that we take our
original price
and 78.9
cents and multiply it by that rate of
discount in decimal form so let's write
that out
78 dollars
and 95 cents
times
35 percent in decimal form so 0.35
so let's calculate that and i'm going to
come to the right in order to go through
those steps now when we multiply
decimals we can take the decimals out
and then place the decimal in the answer
once we get to that point so i'm going
to take the decimals out and multiply
seven
eight
nine five
times
thirty five and again we will worry
about the decimal at the end
five times five is twenty-five
five times nine is forty-five plus two
is forty-seven
five times eight is forty plus four is
forty-four
and then five times seven is thirty-five
plus four is
thirty-nine we are done with this five
and then the two four and four we need
our placeholder zero because we are
moving one place value to the left and
now we can do three times five which is
fifteen
three times nine is twenty-seven plus
one is twenty-eight
three times eight is twenty-four plus
two is twenty-six
and then 3 times 7 is 21 plus 2
is 23
so now we
add here
5 plus 0 is 5. 7 plus 5
is 12
1 plus 4 is 5 plus 8 is 13.
1 plus 9 is 10 plus 6 is sixteen
one plus three is four plus three is
seven
and then we have a two
so now we're ready to place our decimal
so we look back at the original problem
and see how many digits are to the right
of a decimal or how many digits are
behind a decimal well we have 1
2
3
4. so that's how many digits are going
to be to the right of the decimal in our
answer so we can count off
one
two
three
four digits our decimal is going to be
placed in between the 7
and the 6 so we get let me rewrite this
without the lines underneath
so we get
two 27.6325 now we are working with
money so we need to round this to the
hundredths place we have a three in the
hundredths place
look at the digit to the right we have a
two that two says we stay the same so we
are going to get
27
and 63 cents so 78 dollars and 95 cents
times 0.35
i ran out of room here so i'm going to
write it above that gives us
27
and
63
cents
so that's our discount that's how much
money we are taking off the original
price that's 35
of 78. and 95 cents so once we have that
information we can subtract that
discount from the original price so the
original price minus the discount we are
taking the discount off of the original
price
the original price
78
95
and we are subtracting
27
63
so let's see what our sale price is
going to be
now when we subtract decimals we need to
line the decimals up so i'm going to
calculate this to the right so we have
78 dollars
and 95 cents
minus
27.50
and 63 cents so the decimals are lined
up and that's going to line up all of
our places let's start by subtracting
the hundredths so 5 minus 3 gives us two
then we have nine minus six
that's three
we bring our decimal straight down it's
lined up throughout the entire problem
eight minus seven
one and then seven minus 2
which is 5. so we get
51
32 so 51
and 32 cents so that is going to be our
sale price so let me rewrite that 51
and 32 cents
this is our final sale price 51
and 32 cents
so there you have it there's how you
calculate a discount by hand i hope that
helped
thanks so much for watching
until next time
peace
you
