GRE Quantitative Reasoning: Multiple Choice Questions
The oneanswer multiplechoice questions have one and only one correct answer out of a total of five answer choices.
The oneormore answer multiple choice questions may have 5 or more answer choices out of which one or more may be correct. You must select all the answers that are correct. Remember, you will not receive full credit unless you have chosen all the correct answers and no others. Therefore, make sure you fully understand the question and have considered all possibilities before proceeding onwards.
Tips and Tricks for Quantitative Reasoning MultipleChoice:

Process of elimination may be your greatest ally in any standardized test. It is especially important in the GRE multiple answer questions where there can be more than one correct answer. If several answers are obviously incorrect, make a mental note or cross them off. Concentrate on the choices that are likely to be correct.

Learn critical formulas and definitions in advance.

If the math seems time consuming, don’t forget that you have your trusty onscreen calculator!

If the answer you found is not there, chances are that your answer is wrong. Reread the question, check you math, and reevaluate your reasoning.

Working backwards from the answer choices may be a good way to approach certain problems. For example, if the question asks which of the answer choices is farthest away from the number 1 on a number line, go through choice by choice to determine the answer. For inequality questions, you can also plug in the answer choices. Remember though that this method may take more time than reasoning.
Example:
Q. A tower casts a shadow of 6 meters at a certain time of the day. If at exactly the same time, a man stands at the top of the tower, the length of the shadow increases by 2 meters. What is the height of the man if the tower is 5 meters high?
(A) 1 meter
(B) 1.5 meters
(C) 1.66 meters
(D) 2 meters
(E) meters
Answer: C
Solution:
Step 1: This is a simple proportions problem. The basic concept is that when the man stands on the top of the tower, the length of the shadow increases proportionately to total height of the tower and the man. The following figure should make it clear:
Step 2: If we assume the height of the man as x, we can express the proportional relationship mathematically as:
Cross multiplying and simplifying the equation, we get: