o if i not wrong this question type is called inverse dunno wat
de..
i was very lousy at this but later i learnt it this way.. and it
is very effective to me..
how i learnt is was always writing down the info first, for
example in ur case :
1
blanket
mary -----> 6 days
jane -------> 10 days
so later u think, in 1 day, how many blanket can she sew?
1 blanket ------> 6 days
1 day ----------> refer to below
so now u think, mary take 6 day to sew one bloody blanket, then one
day, she sew more blanket than the 6 day? or less blanket than 6
days? think think think...
later u think, o! mary 6 day sew 1 blanket, meaning 1 day she
can sew a bit only.. so is lesser than 1 blanket le..
so mary, 1 day -------> 1 divided by (a number) of
blanket
now u think again, the number would be wat? the number must be
related to mary, related to the number of day right? so now u
think and think, o the number can only be 6 days!
so mary, 1 day -------> 1 divided by 6 of blanket!
now do the same thing for Jane.
mary, 1 day -----> 1/6 blanket
jane, 1 day -------> 1/10 blanket
now time for a simple check if u are right so far, using ur common
sense, would a person take 10 days to sew a blanket, sew more
blanket than a person who take only 6 days to sew a blanket?
so jane take so long to sew a blanket (10 days), obviously sew
lesser blanket in a day than mary who take only 6 days to sew a
blanket
ok so now u check, all u had done so far is correct
so now the question ask u, they sew together, how long they take to
sew a dam blanket?
now u think and think,
mary -------> 6 days
jane ----------> 10 days
both do together ----------> faster than one person or
slower?
of course is faster! now in ur heart, u must visualize that the
answer is lesser than 6.
now, calculate the amount of blanket they can sew in a
day,
mary + jane ------> how many blanket?
now u think, mary and jane dun care each other, they sew their own
thing, then end of that day they combine their blanket, meaning
that the sewing together doesnt affects the speed, they each have
their own speed.
so mary + jane ----------> 1/10 + 1/6 = 4/15
now check again, is 4/15 more than 1/6? if not, try other
numbers and way.. make sure it makes sense. if yes, and it makes
sense (use ur common sense), then good le! u are on the right
track!
now the question ask u how long, not how much blanket, since
they cannot even finish a blanket in a day, they must have took
more than a day to finish sewing this blanket, now think back, ur
answer must be lower than 6 but higher than 1... this is to check
and confirm ur answer...
now do ur working,
1 day -------> 4/15
1 blanket ------> refer again
now i also confuse already, but nvm i got my common sense, now u
got 2 numbers to work with, "1" and "4/15", now how u gonna work
them out in order for them to be bigger than 1 and lower than 6, (
please note that addition (+) and subtracting (-) do not work in
this step, so only left with dividing or multiplying.. but
multiplying 4/15 and 1 is lower than 1 itself.. so u divide 4/15 by
1, the answer is still lower than 1, so u try again 1 divided by
4/15, ok this time u get an answer bigger than 1 lower than 6...
congratz
then write ur working,
1 day --------> 4/15 of blanket
1 full blanket ---------> 1 divided by 4/15 = 3.75 day (remember
to change ur answer to fraction, cuz the question ask u to)
therefore, they both need 3 3/4 day to finish sewing one bloody
blanket.
btw, if i am wrong or have any misconceptions, please please
please tell me, i learnt this not long ago by myself, i do not want
to have any misconception on this as i am having my "o" levels in
the next few months!
if u wan to summarize it, the method for doing this type of
question is common sense, numbers u are working with must be
related, use ur common sense!
IA