faster2015
Hi,
I have an data sufficiency question that I find a smart way to solve in less than 2 minutes. Could you please help..
Mira and Nina can each perform a certain task in m and n hours, respectively.
Ism<n?
(1) Twice the time it would take both Mira and Nina to perform the task together, each working at their respective constant rates, is greater than m.
(2) Twice the time it would take both Mira and Nina to perform the task together, each working at their respective constant rates, is less than nIts a Rate Time distance Quant problem.
Answer is D
Thanks,
Saket

Hi Saket,
the Q can be solved in less than 30 secs, if you can play around with the info provided, and algebrically in 1-1 1/2 min ..
lets see the Q..
Q is .. is m<n?
the statements..
(1) Twice the time it would take both Mira and Nina to perform the task together, each working at their respective constant rates, is greater than m.
info:-the statement can be made to read that time taken combined(M and N) to finish the work
twice is greater than work completed once individually by M...
or
time taken combined(M and N) to finish the work twice is greater than work completed once twice by M2 M..this shows M is faster than N... so m<n..
Algebra:-time taken by both =\(\frac{mn}{(m+n)}\)..
so as per the statement \(\frac{2mn}{(m+n)}>m\)..
so \(\frac{2mn}{(m+n)}-m>0\)
\(\frac{(2mn-m^2-mn)}{(m+n)}>0\)....
or \(\frac{m(n-m)}{(m+n)}>0\)....
so this means ..
if m is positive n>m, and
if m is -ive, m>n..
but m has to be positive, so n>m..
suff
(2) Twice the time it would take both Mira and Nina to perform the task together, each working at their respective constant rates, is less than n
similarly for this statement
Hope it helped