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Folks, let's use a formula that looks like this: which is amount
equals percent
times base
I use something a little different which helps a
lot of people
which is, I draw this triangle out
my is is going to go here, my of is going to go here and my percent is going to go here
I'll get to that in a second
basically the base
is the of
and the amount
is the is
so they're both the same thing, just different ways to look at it
and then
i'll show you in a second but that bar in the middle is going to stand
for division
and the vertical bars is going to stand for multiplication
and here's how i'm going to use those: let's say I'm given the problem
Eight is what percent
of forty eight
So let's say I'm given this
First, I have to identify what's my base is, what my amount is, and what my percent is
and what I need to find
so one of the things you might want to do is plug it into the triangle
and i just go by the words and the problems
eight is what percent offorty eight so i don't have my percent. So remember
percent went over on the right side so that's going to be my x or what i don't
know
my is is eight because eight is
my of is forty eight
because we're finding out eight out of forty eight
then i take
these two numbers and with them, I do whatever the operation the triangle
tells me to do
triangle tells me to divide
division mark there
so what i'm going to do
is divide eight by forty eight
and that's going to be the percentage that eight is of forty eight
We should all be comfortable with dividing the long way
by hand
six percent
try that again
Oh, you're thinking about forty eight divided by eight. They're different things
eight divided by forty eight is not the same thing ast forty-eight divided by eight
the second one is six, the first one is not six
so it's going to give you a decimal
so it's going to give you, I can do it the long way with you guys but it's
going to give the zero point one six
do I need to do that
that's the decimal, i want to find the percent so if i want to
convert a decimal to a percent we just did that in the example
Brittany asked about
I'm just going to move the point to the right two times
this is going to be sixteen
six percent
and that six should be
so that brings me to a note about the triangle formula. Our percent is always
going to be plugged in and calculated in decimal
it's up to us to convert it to percent
so this is always going to be in decimal
same thing for this percent it's up to us to calculate it
in percent
this point sixteen repeating means point one six six six six on forever
point one six six six six six six so when I convert it
by moving it two to the right
i still have that six repeating at the end
so that's why it's sixteen point six repeating
two options i don't know that has the option to
show the repeating symbol on the homework it may not
then the other choices look at the directions and it may tell you to round to a
specific place
do you remember the problem
we can talk about it later
i can look it up or it may be that you got the answer wrong, maybe
but typically speaking, it will tell you to round it or it should have the option
if it doesn't have the option
so again, eight is my is
or if i'm looking at the amount equals base formula, the eight is my amount
the percent is not known and the base is forty eight. Two ways of
looking at the same formula
whether i do it by plugging it into the formula and solving for the percent or
whether i do it by the triangle, I'm going to end up doing the same thing which is dividing
eight by forty eight
let's try another one lets say i have
what number
is ninety percent of
zero point
zero
four five
i'm just going to do my triangle
simple as that
and just plug it into my triangle so do i have
here goes the is the of and the percent
so i have the is
no that's what they're asking. They're asking what number is
so that's going to be my is, do i have my of?
my of is
point zero four five because that's what they're trying to figure out, out of
point zero four five
what number is ninety percent of that
so what's my percent
and if i have to convert that to decimal because everytime i plug it in, its a decimal
what's that as a decimal
so according to this triangle, to figure out ninenty percent of point o four five
i just need to multiply point o four five times point nine
times point nine
and can you do that and tell me what that is
so what this tells me is that point zero four zero five is ninety percent of one
zero zero four five
with these type of questions we should always make an effort to kind of
estimate the answer before we even start
for example
if we're looking for ninety percent of point o four five
i know a hundred percent of point o four five is going to be point o four five
so this represents a hundred percent so ninety percent is going to be close
to that
so point o
four o five makes some sense
if i were looking for a number bigger than a hundred percent, then i would get a
number bigger than point o four five
if i were looking for fifty percent or something less than that, i should get less than
half of point o four five
so it makes some sense to look at the problem and estimate what our answer is going to be
again back at this first problem, eight is what percent of forty eight
i know the answer is not going to be forty or
fifty percent for example because fifty percent of forty eight would be twenty four
so it's going to be something a lot less than fifty percent
it actually turns out to be sixteen point six percent
so it makes some sense to look at the problem and estimate the answer before we even
start
so let's try another one
twelve percent
of what number
is twenty one
do i have my is in this case
my is is twenty one
do i have my of
do i have my percent
that's not a decimal
so I divide twenty one by point twelve
can you do that for me and tell me what you get
he has an answer
check your decimals
you also have an answer
one seventy five
and again, that makes some sense because we're trying to figure out twelve
percent of what number is twenty one
and if we did get one point sixty five
if my answer is one point sixty five that would mean that twelve percent of
one point seventy five is twenty one; and that doesn't make any sense
because twelve percent.. well one hundred percent of one point seventy five would be
one point seventy five, so it doesn't make sense for that number to be bigger
so a hundred seventy five makes a hundred percent because twelve percent of a bigger number like one
point seventy five would be something like twenty one
so again, it makes some sense to estimate this as we're doing it
so i have some for you to try out
What number is twenty five percent of ninety,
ninety five percent of four hundred is what number, fifteen
percent of what number
percent of what number
is two point four
try those and then if three people want to do them, I'll give them the extra points