GMAT problem solving questions are designed more to test your understanding of underlying mathematical concepts than to test your ability to actually carry out quantitative procedures accurately.
Fortunately for many test takers, advanced quantitative topics, such as trigonometry and calculus, are not tested on the GMAT. To score well, you only need to be familiar with basic arithmetic, geometry, and algebra, as taught at the high school level. Any decent GMAT prep book will cover these quantitative concepts.
Problem Solving Tips and Strategies
Read the questions carefully. It is impossible to overstate the importance of careful reading. The most common pitfall GMAT test takers stumble into is answering the question they thought they read, instead of the one the test asked. There is a big difference between a question asking "Which of the following may be true?" and one asking "Which of the following may not be true?" The test writers deliberately include answer choices that correlate to common misinterpretations of the questions.
Use your scrap paper for every question. No matter how easy a question appears, you should utilize your scrap paper. Seeing a calculation on paper will help you avoid easy mistakes and the answer choices designed to exploit them. Remember, once you record your answer on the GMAT CAT, you can't go back and change it. This aspect of the CAT makes this tip even more effective.
Do not get bogged down with complicated or lengthy calculations. We have looked at hundreds of GMAT problem solving questions and found that they are deliberately designed to make such calculations unnecessary. You are overlooking a shortcut if you find yourself getting bogged down in this way.
The "guesstimating" technique is extremely effective on this exam. Most of the time, the answer to a problem-solving question is a value, and the values given in the answer choices will not be very close to each other. As a result, you can save time by 'guesstimating.' For example, if you know the value you're looking for is about 30%, and the answer choices are 4%, 13%, 29%, 47%, and 81%, you can safely guess that the correct answer is 29%. Congratulations – you just saved yourself a lot of time on this question, and avoided getting caught up in a longer calculation that might have resulted in a math error!
Learn how to work backwards. If you are completely stuck on a question, you can always try plugging in an answer choice and work backwards to see if it makes sense. When you use this technique, we suggest starting with the choice giving the middle value. Even if the middle value does not answer the question, it might tell you if you need to go higher or lower. You will have narrowed 5 choices down to 2.
Convert quantities freely. There are often shortcuts available to you if you can recognize relationships between the numbers used in the problems. Keep in mind, the GMAT test writers never haphazardly select numbers for their questions. This technique is especially useful in narrowing down likely answer choices when you feel the urge to pull out a calculator. One easy conversion to remember is that, at least for purposes of the GMAT, π = 22/7.
Use process of elimination as a last resort. The GMAT writers have historically arranged answer choices in ascending numerical value. Even if you are unable to immediately hone in on the correct answer, chances are that guesstimating, working backwards, or some other technique will help you eliminate many wrong choices.
Practice, practice, practice. When you spend time practicing quantitative questions, you internalize these tips and strategies. You will also become very comfortable with the type of questions found on this portion of the test, and will quickly realize whether you need to brush up your skills in any math areas, such as geometry or algebra. After all, when it comes time to sit for the GMAT, you will want to be able to recall certain information – the total number of degrees in the sides of a triangle, the calculation for the area of a circle, etc – off the top of your head.
Problem-Specific Tips and Techniques
There are several distinct types of quantitative problems, each of which can be approached with specific tips and strategies:
Assume diagrams are drawn accurately unless the question specifically states otherwise. Do not, however, rely on your visual judgment to answer these questions. The test writers never allow their questions to be that easily answered. One common mistake is to assume that 2 lines must form a right angle, when this is not specifically indicated in the text. Do not fall into this trap – it is one of the most common mistakes made on the GMAT.
Spend at least 30 seconds reviewing the diagrams. Many implicit facts and numbers can be found inside these illustrations. Due to the computer-adaptive nature of today's GMAT, you will need to sketch out the diagrams on your scrap paper to deduce the implicit facts from the data explicitly given.
Spend at least 30 seconds reviewing the graphs and tables. Graph problems are not meant to require hard math calculations. Instead, they are designed to test your ability to interpret and use information contained in graphs and tables. As a result, you will be well served by closely studying the structure and basic content of the graphs and tables. The axis labels, legend key, and units of measurement are more important to you in understanding and answering the question than the actual data presented.
Make sure you are familiar with bar, circle, and line graphs. These are the 3 graph types most commonly presented on the GMAT.
You can rely on visual estimates for bar graphs and line charts. The test writers will not use visual tricks to deceive you. In fact, you will often times have to trust a visual estimation to determine the correct answer. Note: Visual estimates will not work with geometry questions.
Identification is half the battle. Train yourself to recognize when you're dealing with a "weird" problem, and deal with it accordingly. AdmissionsConsultants defines "weird" as problems that simply test your reasoning skills, not your quantitative skills. These questions are widely considered the most intimidating on the entire exam.
An excellent example of this genre of question is a problem that presents a function you never learned in school. You will greatly improve your odds of answering it correctly by calmly and methodically imitating the "logic" presented in the question. If this fails, you can always work backwards to solve the problem.
Build equations for word problems. When dealing with a word question (such as what happens if trains are traveling at a certain speed), build an equation that will help you understand the question being asked and find the answer. Use obvious letter symbols such a "A" for train A, "B" for Bob's age, etc., to stand for the values you need to calculate.
Don't waste time looking for subtle meanings. You can make reasonable assumptions with these questions. The test writers are not trying to trick you in this way.