The GMAT is a multiple choice exam. This means that no matter what, the right answer is right there in front of you, for each and every question. Moreover, the GMAT tests the speed at which you can select the right answer for a particular question. Not the speed at which you can solve the problem presented in that question.
In some cases (especially when doing the Quant), the quickest way to selecting the right answer is by not trying to solve the problem. Let me give an example:
OG 11 Diagnostic Quant section, #7
A certain club has 10 members, including Harry. One of the 10 members is to be chosen at random to be the president, one of the remaining 9 members is to be chosen at random to be the secretary, and one of the remaining 8 members is to be chosen at random to be the treasurer. What is the probability that Harry will be either the member chosen to be the secretary or the member chosen to be the treasurer?
(A) 1/720
(B) 1/80
(C) 1/10
(D) 1/9
(E) 1/5
... Looks intimidating, right? But before you diligently reach for your high school math texts and look up how to calculate probabilities, and before you let your eyes pop out too much upon seeing the lengthy (half a page long) solution provided in the book, think.
There is absolutely no way for an average (or even a significantly above average) person to do this problem in under 2 minutes. Even if you've seen similar questions before, and know exactly how to do it. Reading the question alone takes time, then setting up the equations and simplifying fractions to arrive at the correct solution - it's a headache, and also completely unnecessary.
The key line in the question is the following:
What is the probability that Harry will be either the member chosen to be the secretary or the member chosen to be the treasurer?
Now, just a basic knowledge of probability (and some common sense) would tell us that Harry's chances of being chosen to be the secretary is slightly less than 1 in 9. Harry's chances of being chosen to be the treasurer is slightly less than 1 in 8.
Since both of these chances satisfy the probability condition, you just add the two together.
~1/9 plus ~1/8 is most definitely greater than any of the answer choices, except E. Therefore, the answer must be E.
*******
Of course, recognizing these types of questions might take some practice, but this is a valid technique that I think should figure into your toolbox for cracking the GMAT. While doing practice questions, I've found that for a significant number of questions, eliminating wrong answers or plugging in solutions let me arrive at the correct answer much more quickly.
Anyway, back to studying for me. Good luck!
