Hi All,

You can take advantage of the answer choices and some math "logic" to get to the correct answer. Let's TEST THE ANSWERS....

We're told that X, Y and K are POSITIVE and that X < Y.

We're also told that 10X/(X+Y) + 20Y/(X+Y) = K. We're asked what COULD be the value of K, which means that there's more than one possible answer. Since the answers are NUMBERS, one of the them MUST be a possible answer.

We can manipulate the given equation into:

10X + 20Y = K(X+Y)

Since all of the variables are POSITIVE, K MUST be between 10 and 20. Here's the proof:

IF.....K=10, then the equation becomes...

10X + 20Y = 10X + 10Y

20Y = 10Y

Since Y is positive, 20Y = 10Y is NOT possible.

Eliminate Answer A

In that same way, K can't be 20 (or greater) because the end equation would be an impossibility.

With the remaining 3 answers, we can TEST the possibilities...

IF...K = 12, then the equation becomes...

10X + 20Y = 12X + 12Y

8Y = 2X

4Y = X

In this scenario, X > Y which is the OPPOSITE of what we were told. This is NOT the answer.

Eliminate B.

IF....K=15, then the equation becomes...

10X + 20Y = 15X + 15Y

5Y = 5X

Y = X

In this scenario, X = Y, which is NOT a match for what we were told. This is NOT the answer.

Eliminate C.

IF....K=18, then the equation becomes....

10X + 20Y = 18X + 18Y

2Y = 8X

Y = 4X

Here, X < Y, which IS a match for what we were told. This IS a POSSIBLE answer.

Final Answer:

GMAT assassins aren't born, they're made,

Rich

_________________

Rich Cohen

Rich.C@empowergmat.com

http://www.empowergmat.com