I agree that the one should pick the easiest way.
but it depends on what u prefer easy..
for me algebra is very easy..
and while picking numbers, u dont always get a certain answer..
anyways.. no issues with your picking numbers soln..
I am just wondering why we are getting straight forward algebra wrong..
there has to be a way to solve it right.. and there must be something we are doing wrong..
I proceeded by equating the x's.. may be we cant do that..
experts can probably help..
krusta80 wrote:neerajkumar1_1 wrote:lol..
prob try the other way arnd..
krusta80 wrote:krusta80 wrote:neerajkumar1_1 wrote:If |x|<>|y|, xy<>0, x/(x+y) = n, and x/(x-y) = m, then x/y= ?
a) 3mn/2
b) 3m/(2n)
c) n(m+2)/2
d) 2mn/(m-n)
e) (n^2 - m^2)/(nm)
This one is probably best solved using substitution.
Let's try x = 2 and y = 3...
n = 2/5
m = -2
x/y = 2/3
a) 3mn/2 = -6/5 NOPE
b) 3m/(2n) = -15/2 NOPE
c) n(m+2)/2 = 0 NOPE
d) 2mn/(m-n) = (-8/5)/(-2-2/5) = (-8/5)/(-12/5) = 2/3 YUP
e) (n^2 - m^2)/(nm) = (4/25 - 4)/(-4/5) = (-96/25)/(-4/5) = 24/5 NOPE
D it is.
2mn/(m-n) = 2*[x/(x-y)]*[x/(x+y)]/[x/(x-y)-x/(x+y)] = [2*x^2/(x^2-y^2)]/[(x^2+xy-x^2+xy)/(x^2-y^2)] = 2*x^2/(2xy) = x/y
I must admit that I tried doing so the other way...I ended up with a formula containing n and m, but it did not seem to match choice D. Obviously there must be a way to do it, but I think you may be missing the point anyway.
This is a classic question where using the easiest method to solve it saves tons of time.
