Addition and Subtraction of Fraction - Fractions and Decimals , Maths, Class 7 Video Lecture

hello friends this video on fractions
and decimals part four is brought to you
by exam for comm know about fear from
exam now let us look at addition of
fractions how do we add fractions now
addition of fractions this is something
which you have learnt in detail in your
junior classes but still we will have a
quick recap that how do we add fractions
now again there can be two scenarios
first scenarios scenario could be adding
like fractions that is fractions with
same denominators now let in in that
case the your job is pretty simple let's
say you have one fraction as 6 by 15 and
you have another fraction say 9 by 15 so
how do you add them you just need to do
one thing you need to add the numerators
because in the result also the
denominator is going to be the same so
the numerator would be 6 plus 9 which is
equal to 15 by 15 which is equal to 1 so
this is how we add fractions with same
denominators what about fractions with
different denominators that is the
unlike fractions for example do you have
one fraction 6 by 15 and the other
fraction is 9 by 5 so they have
different denominators so here also we
will follow the same approach we are
going to convert them into like
fractions how do we convert them into
like fractions again we will take LCM of
5 and 15 that is you take the LCM of the
two denominators and what would be the
LCM of 5 and 15 this is how we find LCM
right 5 ones a 5 5 3 is a 15 in 3 ones a
3 so the LCM would be 5 into 3 which is
equal to 15 so the LCM of 5 and 15 is 15
right so once you have taken the LCM
this LCM is going to be the denominator
in the result so this would be 15 now
what do we do is 6 by 15 so 15 into 1 is
15 so therefore what
you will 6 into 1 plus 5 into 3 is 15 so
in the numerator we do 9 into 3 so this
is the approach that we follow very
simple first find out LCM the LCM of the
two denominators would be the
denominator in the result and in the
numerator you find out what is that
number which when multiplied by the
denominator of this fraction will give
this LCM and then you multiply that
number with the numerator in this case
15 into 1 is equal to 15 so we
multiplied 1 to 6 5 into 3 is equal to
15
therefore we multiplied 3 to 9 so this
would be 6 into 1 is 6 plus 9 into 3 is
27
divided by 15 so 27 plus 6 would be 27
plus 6 would be 33 divided by 15 so 33
by 15 would be the sum of these two
fractions so this is how we add
fractions now let us look at subtraction
of fractions that also is done in a
similar way so when you have fractions
with same denominators like say let's
say 6 by 15 minus 9 by 15 in that case
the denominator will remain the same
we just need to subtract the numerators
that is 6 minus 9 which is equal to
minus 3 by 15 so this would be the
result and when you have fractions with
different denominators like 6 5 15 and 9
by 5 so in this case again you find out
the LCM of 5 and 15 so just now in the
previous slide we found out so just now
in the previous slide we found out that
LCM of 5 and 15 is 15 so 6 by 15 minus 9
by 15 this is equal to denominator would
be 15 now 15 into 1 is 15 therefore 6
into 1 minus 5 into 3 is 15
nine into three so this would be six
minus 27 divided by 15 so this would be
equal to minus 21 divided by 15 so this
is the result of subtraction so for
addition and subtraction so once an
animal when they have when both the
fractions have seen denominator it is
pretty simple that is you directly add
or subtract the numerators but when you
have different denominators you take the
LCM of both the denominators and then
you proceed with the addition or
subtraction so basically this is how we
add or subtract fractions thank you
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