L13 : Increase Decrease Percentage - Comparing Quantities , Maths, Class 7 Video Lecture - Class 7 | Best Video for Class 7

hello friends this video on comparing
quantities 5:13 is brought to you by
example calm no more fear from exam so
now that we have learned a lot of
operations with person'd now let us try
to understand increase or degrees in
terms of person so what do we mean by
increase or decrease now have you
observed that when you were in class 2
and now that you are in class 7 your
height would have increased quite a lot
right so if you say that my height so
that increase in height how do you
define that increase in height in
percentage let's say if you say that my
height increased by 10% in the last 2
years that means whatever my you me
earlier height was on top of that there
is a 10% increase or if you see that I
spend not you maybe somebody who's
working so if you say that I spent 40
percent of my salary in 10 days so
basically is talking about how much
money does these spends in the first 10
days he spends what the percent of the
salary in 10 days so basically what is
happening in the first case your height
is increasing and you are denoting that
increase in percentage in the second
case what is happening as you are
spending 40 percent of your salary what
is happening to the bank balance that
you have that is gradually decreasing so
so the salary that you had received
which had made your bank balance so that
the bank balance is gradually decreasing
so here we will see how do we actually
represent the increase or decrease in
some quantity in terms of percentage so
we will see how do exactly convert
increase or decrease as percentage so
for this let us we will consider an
example so increase or decrease in any
quantity is always calculated as a
percentage of the initial amount this is
very important so whenever you want to
express increase or decrease of
in terms of percentage so that that
should happen on that initial amount
because the change is happening on the
initial amount right for example earlier
you are high towards 130 centimeters now
your height is 150 centimeters so
basically this increase has happened on
your initial height on your existing
previous height right so the person is
always is calculated on the initial
amount this is one very important point
to be understood and remembered so let
us take an example so here we see a
mother-daughter dwarf and the mother
says that in my childhood patrol was
rupee one per liter so the cost of
petrol and used to be rupee one for one
detail so this was the before scenario
this is how it was initially so before
rupee one for one liter of petrol and
then the daughter sees that it is rupees
fifty two per liter today so what is it
now so now the price is rupees fifty two
for one liter so what do you think what
has happened whether the quantity has
increased or decreased so the quantity
here is the price because the price is
undergoing a change so the price has
increased from rupees one two rupees
fifty one so here we see an increase in
the quantity so how do we do it present
this increase in percentage so for that
first of all we need to find out how
much is the increase so how much is the
increase the increase would be the
difference between these two values that
is rupees fifty two minus rupee one
which is equal to rupees fifty one so
this much is the increase but we need to
represent this increase in percentage so
percentage increase would be equal to
the actual increase here the actual
increase is rupees fifty one divided by
the original price or the initial price
whatever you call it the initial price
in two hundred percent so this in two
hundred percent is just to convert the
fraction
to percentage so why did it we divided
it by the initial price because that is
what I told right that percentage of
increase or decrease will always be
calculated out of the initial amount
because whatever increase or decrease
has happened in if it has happened on
the initial amount so initial amount was
rupee one so this increase has happened
over rupee one so how much that increase
is in order to know that you actually
need to divide the increase by the
initial price so this would be equal to
fifty one by one in two hundred so this
would be equal to fifty one hundred
percent so this basically tells you that
in these many years the price of the
Patrol has actually increased by fifty
one hundred percent so that's like a
huge increase right so this is how they
actually convert increase or decrease in
terms of percentage so this is something
that you do know let us try this out
find percentage of increase or decrease
if the price of shirt decreased from
rupees eighty
to rupees 60 so with what was the
initial price so the initial price was
rupees eighty and what is the later
price or the decreased francs because
there clearly we can see that the price
has reduced from eighty to two peas
sixty sorry so how much is the actual
decrease so the actual decrease would be
the difference between these two that is
80 minus 60 which is equal to rupees 20
so now when you have to calculate the
percentage decrease that would be equal
to the actual decrease divided by the
initial price multiply it by 100 percent
so this would be equal to 20 divided by
80 into
hundred so this would be equal to 25 so
we would say that there was a 25%
decrease in the price of the shirt thank
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