Bunuel wrote:

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

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

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)

This question was discussed before, please refer to the other approaches at:

what-is-the-value-of-k-85382.html#p640124Thanks for the solution and the pointer to the earlier thread.

I'd run a search but didn't hit that thread... maybe due to the mathematical formula.

hit a roadblock right in the first step of simplifying the equation... \(10(x+2y)/(x+y)\)

But now understood the approach