Examples: Ratios and Proportion Video Lecture - Class 7

hello friends this video on comparing
quantities part 5 is brought to you by
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system what even basic things we have
learnt about ratios let us quickly have
a look at some of the questions question
number 1 find the ratio of 30 days to 36
hours ok so these are the two quantities
which we need to compare so this is our
quantity 1 this is our quantity 2 now do
you remember one of the important
criteria of writing ratios that both
these quantities must have the same unit
must have same unit so in case of
quantity 1 the unit is days in case of
quantity to the unit is hours so we need
to convert one of these into the other
so that both of them are in the same
unit so let us say what is our quantity
1 so quantity 1 is 30 days let us
convert 30 days in two hours now one day
is equal to 24 hours in one day is equal
to 24 hours
therefore 30 days would be equal to 30
into 24 hours right so 30 days can be
written as 30 into 24 hours this is
equal to 720 hours now let us look at
quantity - so quantity 2 is already
given in hours so now you see we have
both the quantities in the same unit
right so therefore the ratio of quantity
1 to quantity 2 would be quantity 1
divided by quantity 2 so this is equal
to 36 to 72 0 so this is 20 divided by 1
so this can be written as 20 is 2 1 so
this is the ratio question number 2 in a
computer lab there are three computers
for every
students how many computers will be
needed for 24 students now do you
remember the unitary method which you
had learned in your junior classes so if
you remember then it's super nan good in
case you have forgotten I'll remind you
about the unitary method so what was
this method all about this method always
asked us to find out the value for one
unit and then find out the value for
multiple units what does that mean let
us try to solve this question and then
understand so the question says that
there are three computers for every six
students that means for six students the
number of computers that are present are
how many so for six students there are
three computers that means you really do
not have even one computer for one
student one computer needs to be shared
between what two students so basically
for one student how many computers do
you have so if the total number of
computers is say 3 4 6 students then for
one who student the number of computers
that you have is 3 by 6 which is nothing
by 1 by 2 so half a computer is for one
student basically now the question asks
for 24 students
therefore for 24 students the number of
computers would be for one student it is
3 by 6 so for 24 it would be 3 by 6 into
24
so 6 fours or 24 and 4 3 sir
12 so basically 12 computers are needed
for 24 students now what does this
unitary method so the concept is that
first we find the value of one unit so
first we found the value of computers
that is the number of computers needed
for one student that is one unit and
then the value of required number of
units so here the required now
of Units when 24 students first we found
the number of computers needed for one
student and then we multiplied it by 24
to find out the number of computers for
24 students so this is a very basic
method which is used for various
calculations where we want we are given
a certain value for a certain number of
units and we have to find out the value
for some other number of units so
everywhere what we do is we find the
values one unit and then we multiply it
by the required number of units question
number three population of Rajasthan is
570 labs and population of UB is 1660
lakhs in yog Rajasthan is 3 lakh
kilometer square and area of u P is 2
lakh kilometer square how many people
are there per kilometre square in both
these things okay
so let us try to calculate this so how
many people per kilometer square that
means per kilometre square means how
many people are present in one kilometre
square so that is what we need to find
out so let's see how to be proceed so
let us first look at Rajasthan so for
Rajasthan area of Rajasthan is 3 lakh
kilometer square so in 3 lakh kilometer
square area how many people are present
so this is the total area of Rajasthan
and in the total area of Rajasthan
resides the total population of
Rajasthan right so that means 3 lakh
kilometers to any area accommodates 570
lakhs people right so now we have to
find out 1 kilometer square so that is
one unit that is what we have to find
out per kilometer square how many people
resides so in 1 kilometer square the
number of people that would
would be 5 70 lakhs / 3 lakhs so this
would be equal to 190 people so these
many people would recite per kilometre
square in Rajasthan so this was about
Rajasthan so let us now look at you pee
what's happening in you pee so in you
pee the total area is 2 lakh kilometer
square and this total area of 2 lakh
kilometer square is accommodating 1 6 6
0 lakhs people so 16 60 lakhs people so
that means 1 kilometer square would
accommodate how many people 1 6 6 0
lakhs
/ 2 lakhs so this is 2 8 16 2030
so this would be 830 people so when you
see in Rajasthan in 1 kilometer square
190 people recites whereas in you pee in
1 kilometer square 8 30 people decides
so what would you say with steel is less
populated so definitely less less
populated would be Rajasthan because
here you have less number of people
within one kilometer square thank you
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