If x, y, and k are positive numbers such that [x/(x+y)](10) + [y/(x+y)] (20)=k and if x<y, which of the following could be the value of k? (A) 10 (B) 12 (C) 15 (D) 18 (E) 30 The answer is (D), but I'm not sure about all the steps in the process to get that answer. Some of the steps to get that an...

I've got as far as finding K, which is equal to 10 + [10y/(x+y)]. And I know 0 < x <y, but I'm not sure on the next steps after this.

Never thought of it that way but thanks for your help.

There's usually more than 1 way to work out a problem. If I wanted to approach this problem from another angle, any examples of how i would do this, and\or tips.

That approach is the simplest. Thanks for the reply.