GMAT Problem Solving (PS) | Re: If x, y, and k are positive numbers such that (x/(x+y))(10)

\(10*\frac{x}{x+y}+20*\frac{y}{x+y}=k\)

\(10*\frac{x+2y}{x+y}=k\)

\(10*(\frac{x+y}{x+y}+\frac{y}{x+y})=k\)
Finally we get:\(10*(1+\frac{y}{x+y})=k\)


We know that\(x<y\)

Hence\(\frac{y}{x+y}\) is more than \(0.5\) and less than \(1\)

\(0.5<\frac{y}{x+y}<1\)
So,\(15<10*(1+\frac{y}{x+y})<20\)


Only answer between\(15\) and\(20\) is\(18\) .

Answer: D (18)
There can be another approach:

We
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