Friday, May 23, 2008

GMAT Math - Problem Solving Tutorial

GMAT Math : Problem Solving (PS)

The quantitative section on the GMAT consists of two parts :
1. Data Sufficiency - Discussed in the earlier post)
2. Problem Solving - We are going to talk about it today

Quantitative Problem Solving on GMAT :
The Problem Solving questions make approximately 2/3rd of all the questions on the GMAT Quantitative Section. They are therefore of utmost importance to get you a higher score. Although the Problem Solving questions belong to the easy category of maths, you need to be very careful while solving them as they would be quite tricky.

On this question you will be given a math problem and five answer choices. You would have to work out the problem and choose the best answer. Timing is very critical on this question. You would have 75 minutes to solve 37 question in the quantitative section of GMAT. Hence you need to be very quick on the Problem Solving section as this is the easy one. Another important point here is taking shortcuts. With the time limit of 75 minutes you would be in a comfortable position if you try solving problems in less time rather than trying to solve them methodically. Therefore techniques like plug in and back tracing would be useful here. I will discuss them in more detail later. The problems on this section would be divided into basic arithmetic, algebra, geometry and word problems. We will discuss each of them in subsequent sections.

TIPS and Strategies for GMAT Problem Solving

This section requires you to solve problems on algebra, geometry and arithmetic, simple probability and permutations and combinations. There are around 17 problem questions out of 37 quantitative questions.

• Most Imp Tip : Based on our students experience, some questions are very easy so one should only spend only about half a minute and some 4-5 questions are tricky and one has to spend 3-4 minutes to crack those tough questions. Some students couldn't complete the quantitative sections and most of them felt that they should have done the easier questions faster rather than revising those easy ones again and again

• Read the question carefully. Some times they just add negate the positive statement say for example they may ask which of them was not true? By making this a habit one can save 2-3 silly errors.

• Use paper and pencil for short calculations and for taking note of eliminated choices.

In GMAT answer choices are arranged in ascending or descending order so while guessing an answer or while working backwards one should always start from choice b or d as it will tell u in which direction u should move and may save a step or two ( same principle is followed in Binary index searching).

• Do not waste time on lengthy calculations as GMAT questions are mostly based on tricks and they do not expect you to go on lengthy calculations. One may spend some time on trick else it is better to leave the question. Sometime it may be a test question for future GMAT ( Out of 37 question in gmat only 28 are evaluated and rest are future test questions to understand their difficulty level based on your correct answers and time spent).

• GMAT expects to you to do approximations as answers choices are rarely close. say 9.5 can be rounded of to 10 or 22/7 can be assumed to be 3.

• In GMAT if you are weak on certain specific question types then do make notes and just practice those questions again and again so that one can save time on those questions. Some examples are given below

- Practice the set question up to 3 level example three sets of people doing different things etc say 20 people do x and y, 10 people y and z and 5 people x,y and z

- Practice downstream and upstream questions for example one elevator going down and other coming up when they will meet.
- No of diagonals in a polygon ( N* C* 2 - N )
- Questions on probability. 5 coins are tossed together etc
- One people finish work in x days, 2 people in y days how many days the other person will do etc-2.

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.

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.

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!

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, p = 22/7.