One way that i would do this problem is as per the following:

****Use the strategy of checking the answers from bottom. ie. from E*********

I always use this strategy and this works.......


Simply the problem, (10x+20y)/(x+y) = k

now substitute 30 for k, and find out whether the x<y condition satisfies

Start with E (as per the strategy)

10x+20y=30x+30y
20x=-10y
x=-0.5y .........condition is not being satisfied

now move to D,

10x+20y=18x+18y
8x=2y
x=0.25y .........condition is being satisfied

Now you can stop and there is no neccessity to check other choices

and D is your answer

bek_gmat wrote:Can anyone (preferably Experts) tell me what level question is that in terms of GMAT score? And OG explained the answer in a much more complicated way, i'm sure anyone try that in exam would run out of time, so if anybody has a shortcut solution to the problem, feel free to share.

OG 12edn: #148

If x, y, and k are positive numbers such that

(x/x+y)10+ (y/x+y)20= k, if x<y, what could be the value of k?

(A) 10
(B) 12
(C) 15
(D) 18
(E) 30

The answer is D

I posted an explanation here:

https://www.beatthegmat.com/tough-algebr ... 13568.html