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GMAT Preparation: How to master the Art of Guessing on GMAT Maths

Written by Sameer Kamat

The GMAT syllabus can appear to be vast and scary. So preparing for the GMAT test involves more than just knowing every GMAT verbal and quantiative concept perfectly. Knowing how to guess intelligently on difficult GMAT questions can save you time and get you some good scores too. In the GMAT preparation series written by GoGMAT for MBA Crystal Ball, this week’s focus is on how to sharpen your guessing skills with some cool tips and tricks.


GMAT Preparation – The Art of Guessing

During the Quantitative section of the GMAT, you may encounter problems that you cannot solve straightforwardly. It is impossible to skip such questions because GMAT is an adaptive test; you are required to give an answer before going to the next problem. You will have on average two-minutes for each problem, and it is highly recommended that you follow this pace because any questions you leave unanswered will result in a penalty. Given these time constraints, you almost certainly will have to guess on some problems. Try to make sure your guesses are not random but educated.

Your most powerful tool for educated guessing is the Process of Elimination (PoE). The idea of this method is that you eliminate answer choices that are clearly wrong, thereby increasing your chance of choosing the right one. For instance, if you can eliminate two of the five answer choices, your chance to choose the right one increases by 65% (from 20% to 33%). This process works exceptionally well when, for example, you cannot calculate the exact value of the correct answer, but you know it must be a positive integer. In such a case, you can eliminate answer choices that are negative or are non-integers. You also should eliminate answer choices that are identical, even if they are written in different ways; no GMAT problem has more than one correct answer.

PoE works better if you use scratch paper. For every problem, draw a column of answer choices:

A
B
C
D
E

Then cross out those that are wrong or just seem too weird.

Which of the numbers below is a prime number?

  1. 5436
  2. 2381
  3. 3994
  4. 7515
  5. 1598

The only even prime number is 2. Thus, you can eliminate A, C, and E.

7515 is divisible by 3 because 7+5+1+5=18 is divisible by 3. So you can also eliminate D, leaving only B.

PoE is also applicable for Data Sufficiency problems. For example, if one of the statements is true, then you can cross out answer choice E. If neither of them is true, you can eliminate D.

Never eliminate an answer choice simply because you selected it on a previous problem. It is possible that the same choice will be the correct answer to several successive problems.

Backsolving is another method of educated guessing. To use this method, plug the answer choices into the problem one by one. Only the right choice will be fully consistent with the question. Please note that this method is applicable only to Problem Solving questions with numerical answer choices. You should also note that it is very time-consuming because you need to repeat a set of operations for each answer choice. However, this method is handy for some text problems, in which you can determine whether the right answer is greater or smaller than the choice you have tested. Let’s look at a simple problem.

Jane earns $15 per hour at her day job, and $20 per hour at her night job. Each week she works four times more hours at her day job than she does at her night job. If she earns a total of $800 each week, how many hours does she work per week at her night job?

A. 10
B. 15
C. 20
D. 25
E. 40

This problem can easily be solved with algebra, but let’s try to do it with backsolving. First, plug any answer choice into the condition. Let’s start with B. If she works 15 hours at her night job, then she works 60 hours on her day job. Hence, her weekly salary is 20*15+15*60=1,200. This answer is greater than $800, and you should take the answer choice that is smaller. So the right answer is A.

Please note that in the problem above we started with answer choice B. Why? Because by testing B, we increase the chance of finding the right answer immediately. Not only is it possible that B is the correct answer, but also we can definitely choose A if B is too big, as in the example above. The same logic works with D and E.

There are several other techniques you can use to optimize your guessing. One of them is known as Matched Sets. If two of the answer choices are connected somehow, one of them will likely be the right answer. Here is a list of the most frequent cases:

  • If 1 and -1 are among the answer choices, one of them is likely to be the right answer.
  • When dealing with fractions and percentages, if you can see answer choices that total 1 (or 100%), for example 2/7 and 5/7, the right answer is likely to be one of them.
  • If you are asked to find x-10 and there are two answer choices that differ by 10, chances are that one of them (the smaller one) is correct.
  • If you are asked to find some quantity in kilometers, and there are two answer choices that differ by 1000 times, the right answer is probably one of them.

You should understand that the test-makers know all the techniques presented here and try to make the answer choices look very attractive to test-takers, but these are traps. The only way to become proficient in educated guessing is to practice it a lot.

Continue learning on our GMAT discussion forum. If you have any GMAT related questions about this post or any other GMAT topic, head over to the GMAT preparation helpdesk and shoot your queries.


GMAT Preparation Tips by GoGMAT
GoGMAT, founded in 2009, is an adaptive GMAT preparation platform developed by the best instructors in the industry (with 740+ GMAT scores and strong teaching experience). Find out more here: GMAT preparation courses


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Sameer Kamat

About Sameer Kamat

Founder of MBA Crystal Ball | Author of Beyond The MBA Hype & Business Doctors Connect with me on Google+ | Twitter @mba_cb | Facebook

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