Problem Solving

If anyone has their OG 12 book handy, I'd like to know if there is a shortcut to solving any problem related to #148 in the Problem Solving section (page 173).

I get about half-way through the simplification/factoring of the initial formula, but then the "official answer" explains further steps to take that I simply/honestly never would have thought of - especially in a 2-minute time allotment.


In other words, how can I tackle such questions that give you three variables,...then tack on a "x < y" expression....and then list integers as the answers?

Many thanks....

These kind of variable questions should be answered backwards, i.e. use the answer choices to answer the question.

The equation can be simplified as:
==> 10(x+2y)=k(x+y)

Start by plugging in the value of C (i.e.15). You will see that the equation solves to x=y. But, the question stem says that x<y. So, this and any value less than 15 cannot be the answer. Plugging in the value of D (i.e. 18), you get y=4x. This is very much possible. Check with the value of E & you will get 2x+y=0. This means that x or y has to be a negative value, but they are positive numbers (according to the question stem).

So, D is the answer.