Examples: Properties of Multiplication of Integers Video Lecture - Class 7

II hello friends this video on integers
part 16 is brought to you by exam for
calm no more fear from exam question
number 4 find the product using suitable
properties - 57 into minus 19 plus 57
now this thing can be written as minus
57 into minus 19 plus 57 into one you
can write this like this because 57 into
one is 57 57 can be written as 57 into
one by looking at this do you remember
any property yes of course
it reminds us of the distributive
property so as for the distributive
property a into B plus C is equal to a
into B plus 2c so right now we have it
in the format a into B plus a into C
okay so we have it in that format more
or less so what do we do we can write it
as something like this we can write it
as a into B plus C what is C C is
nothing but 1 now you might be wondering
where did the negative sign go that's
because this is negative this is also
negative so negative negative will
become positive so whenever you multiply
two negative numbers the sign of the
product is always positive so we have
ignored the negative signs so from this
what you can say this would be equal to
57 into 20 now multiplying this is easy
you have a zero so you put a zero
straight forward now 57 into two so this
is one one four zero so you see by
making use of properties we can simplify
the calculations
question number five in a class test
containing ten questions five marks are
awarded for every correct answer and
minus two marks are awarded for every
incorrect answer and zero for questions
not attempted Mohan gets four corrected
six incorrect answers
what is his score okay so as far as
Mohan score is concerned he has given
four correct answers so four four
correct answers what would be his hole
so five marks are awarded for every
correct answer so four four correct
answer his code would be 4 into five
four six
incorrect answers what would be his
score for every incorrect answer two
marks are deducted so 6 into minus two
because these marks are deducted
therefore the total score of Rohan would
be 4 into 5 that is the correct answer
score plus the incorrect answers code so
this would be 20 minus 12 which is equal
to 8 therefore Mohan score would be 8 so
let us look at the second part where it
says that Reshma gives five correct and
five incorrect answers so for five
correct answers the score would be five
into five and four five
incorrect answers the score would be 5
into minus 2 therefore the total score
of Reshma would be 5 into 5 that is
correct answers plus 5 into minus 2 that
is incorrect answers so this would be 25
minus 10 which is equal to 15 similarly
in the third case we see that Hina gave
two correct answers five incorrect and
seven did not attempt so that means for
two correct answers the score would be
two into five for five
correct answer the score would be five
in two minus two and four seven
questions which were gone not attempted
the score would be seven into zero
therefore the total score would be 2
into 5 that is the correct answers plus
5 into minus 2 that is incorrect answers
plus 7 into zero so this would be equal
to 10 minus 10 plus 0 so this is equal
to 0 so the next score of hina would be
0 question number 6 a certain freezing
process requires that room temperature
will be lowered from 40 degree Celsius
at the rate of 5 degree Celsius every
hour so that means the room temperature
currently is 40 degree Celsius and we
want the room temperature to decrease so
what will be the room temperature 10
hours after the process begins so after
10 hours what would be the temperature
when the temperature is decreasing at
the rate of 5 degree Celsius every hour
so after every 1 hour the temperature
reduces right by 5 degree Celsius again
after 1 hour 5 degree Celsius again
after 5 hour minus 5 degrees so that is
how it is reducing and what should be
the temperature at the end of 10 hours
so that means in 1 hour what is the
decrease in one hour the decrease is 5
degree Celsius
therefore in 10 hours what would be the
decrease the decrease would be 5 into 10
degree Celsius right so therefore what
would be the final temperature so the
final temperature would be 40 degree
Celsius because this much temperature
will decrease and what is the current
temperature current temperature is 40 so
the final temperature would be 40 minus
5 into 10 right so this would be 40
degree minus 50 degree which is equal to
minus 10 degree say
because this much would be this 5 into
10 which is equal to 50 degree searches
with three degrees anxious would be the
total decrease in temperature this much
the temperature will decrease so what
would be the final temperature 40 that
is the initial value minus whatever has
decreased that is 50 so 40 minus 50
would be the final temperature we
replace the blank with an integer to
make it a true statement minus 3 into -
is equal to 27 so you see this is
negative but the product is positive
that means this should also be negative
only then the product would be positive
so 3 into 9 is 27 in this case this is
positive and this is negative that means
this has to be negative that 5 into 7 is
35 so this will be by yourself thank you
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