Solving 3 Simultaneous Equations Questions

[Guest]

Regarding questions on solving 3 Simultaneous Equations (like the one in the Equations, Inequalities & VICs guide, pg 21 #6), when presented with 3 equations (with 3 variables), what is the easiest way to combine them?

I.e. Is there a way to know which 2 out of the 3 equations to combine, or you have to rely on trial-and-error? In addition, when combining 2 equations, which variables should be usually solved for?

I basically seem to always pick the most complicated equations (or variable) to combine, and always get stuck!

Thanks!

[StaceyKoprince]

Good question! I don't have my book handy and can't look at that specific problem, but I can give you some general guidelines. (And if you do want us to comment on that particular problem, please go ahead and type it in!)

First, you don't often get 3 simultaneous equations on this test, so don't worry about it too much.

Second, take a look at what the problem wants before you decide how to approach it. You won't be asked to solve for all three variables, the way you would in math class. Often they'll want some combination of variables (for example, what is x+y?). You should keep in mind then that you are trying to solve for the combination x+y, NOT for x and y individually (that takes a lot longer and sometimes, depending on the problem, it's actually impossible to solve for x and y individually even when you can solve for the combination x+y).

Then look at your three equations and try to visualize how you could manipulate them to leave you with the specific combination that you want. Don't spend too much time at this - just dive into it if you don't see anything obvious. But do take 10-15 seconds to see if you can figure something out.

The problems in the in-action problem sets in the book are not trying to mimic GMAT problems - they're actually more like pure math textbook problems, designed to see whether you know the actual math. So I wouldn't worry too much about something like that if it's really giving you trouble, because the "real" math is a lot more complicated (in this instance) than what the test would give you. For example, with simultaneous equations on the test, you often don't have to multiply the equations by anything before you add or subtract - whereas, in real math, you almost always have to do that.

Just focus in on what they asked and aim for that. Also remember that if the answer choices are in terms of variables, you can just try substitute in real numbers and do arithmetic instead of algebra! (The VIC technique)

[Guest]

This makes me feel alot better! As I have been struggling with some of the in-action problems. It's a good feeling to know that these problems are pure math, and that the problems on the exam are a little easier to solve. Thanks!

[StaceyKoprince]

Well - sometimes easier, sometimes harder. :) The "pure math" on the test is easier than it is in that particular example. The way they ask a question, though, can sometimes be pretty darn hard...