GMAT Probability Problems
Posted on
12
Aug 2021

GMAT Probability Problems – How to Tackle Them & What Mistakes to Avoid

By: Apex GMAT
Contributor: Ilia Dobrev
Date: August 12, 2021

The concept of probability questions is often pretty straightforward to understand, but when it comes to its application in the GMAT test it may trip even the strongest mathematicians.

Naturally, the place to find such types of problems is the Quantitative section of the exam, which is regarded as the best predictor of academic and career success by many of the most prestigious business schools out there – Stanford, Wharton, Harvard, Yale, INSEAD, Kellogg, and more. The simple concept of probability problems can be a rather challenging one because such questions appear more frequently as high-difficulty questions instead of low- or even medium-difficulty questions. This is why this article is designed to help test-takers who are pursuing a competitive GMAT score tackle the hazardous pitfalls that GMAT probability problems often create.

GMAT Probability – Fundamental Rules & Formulas

It is not a secret that the Quantitative section of the GMAT test requires you to know just the basic, high-school-level probability rules to carry out each operation of the practical solution path. The main prerequisite for success is mastering the Probability formula:
Probability = number of desired outcomes / total number of possible outcomes

Probability = number of desired outcomes
total number of possible outcomes

We can take one fair coin to demonstrate a simple example. Imagine you would like to find the probability of getting a tail. Flipping the coin can get you two possible comes – a tail or a head. However, you desire a specific result – getting only a tail – which can happen only one time. Therefore, the probability of getting a tail is the number of desired outcomes divided by the number of total possible outcomes, which is ½. Developing a good sense of the fundamental logic of how probability works is central to managing more events occurring in a more complex context.

Alternatively, as all probabilities add up to 1, the probability of an event not happening is 1 minus the probability of this event occurring. For example, 1 – ½ equals the chance of not flipping a tail.

Dependent  Events vs. Independent Events

On the GMAT exam, you will often be asked to find the probability of several events that happen either simultaneously or at different points in time. A distinction you must take under consideration is exactly what type of event you are exploring.

Dependent events or, in other words, disjoint events, are two or more events with a probability of simultaneous occurrence equalling zero. That is, it is absolutely impossible to have them both happen at the same time. The events of flipping either a tail or a head out of one single fair coin are disjoint.

If you are asked to find a common probability of two or more disjoint events, then you should consider the following formula:

Probability P of events A and B   =    (Probability of A) + (Probability of B)

Therefore, the probability of flipping one coin twice and getting two tails is ½ + ½.

If events A and B are not disjointed, meaning that the desired result can be in a combination between A and B, then we have to subtract the intersect part between the events in order to not count it twice:

Probability P of events A and B   =    P(A) + P(B) – Probability (A and B)

Independent events or discrete events are two or more events that do not have any effect on each other. In other words, knowing about the outcome of one event gives absolutely no information about how the other event will turn out. For example, if you roll not one but two coins, then the outcome of each event is independent of the other one. The formula, in this case, is the following:

Probability P of events A and B   =    (Probability of A) x (Probability of B)
How to approach GMAT probability problems

In the GMAT quantitative section, you will see probability incorporated into data sufficiency questions and even problems that do not have any numbers in their context. This can make it challenging for the test taker to determine what type of events he or she is presented with.
One trick you can use to approach such GMAT problems is to search for “buzzwords” that will signal out this valuable information.

  • OR | If the question uses the word “or” to distinguish between the probabilities of two events, then they are dependent – meaning that they cannot happen independently of one another. In this scenario, you will need to find the sum of the two (or more) probabilities.
  • AND | If the question uses the word “and” to distinguish between the probabilities of two events, then they are independent – meaning their occurrences have no influence on one another. In this case, you need to multiply the probabilities of the individual events to find the answer.

Additionally, you can draw visual representations of the events to help you determine if you should include or exclude the intersect. This is especially useful in GMAT questions asking about greatest probability and minimum probability.

If you experience difficulties while prepping, keep in mind that Apex’s GMAT instructors have not only mastered all probability and quantitative concepts, but also have vast experience tutoring clients from all over the world to 700+ scores on the exam. Private GMAT tutoring and tailored customized GMAT curriculum are ideal for gaining more test confidence and understanding the underlying purpose of each question, which might be the bridge between your future GMAT score and your desired business school admissions.

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Posted on
22
Jan 2021

GMAT Test Day FAQs

Should I Arrive Early at the Test Center on Test Day?

Yes, you should arrive early at the test center as there is a check-in procedure that you have to go through before taking the exam. Make sure to be there at least 30 minutes early. If you are 15 minutes late on test day, the administrators may not allow you to take the exam. 

What is the Check-in Procedure? 

Once you show up at the test center, you have to present a valid GMAT approved photo ID to the administrators. Then, they will take your picture, signature, and fingerprints and they will ask you to sign the GMAT Examination Testing Rules & Agreement as part of the check-in procedure.

What documents should I bring to the test center?

There are 2 things you’ll definitely need with you on exam day. Firstly, make sure to bring your GMAT approved photo ID which contains your name, your date of birth, a recent photograph, and your signature (a passport, a national ID card, or a driving’s license). You will not be allowed to take the GMAT if you don’t present that document. Another thing to definitely bring with you on test day would be your appointment confirmation letter or email. It is not necessary that you bring that with you, however, it is good to have it on you in case of a misunderstanding or mistake in the system.

Pro tip: It is also a good idea to bring a list of up to 5 MBA programs that you want your scores sent to. You don’t want to have to decide that on exam day.

What am I Allowed to Bring Into the Exam Room?

You are not allowed to bring anything with you into the exam room, as everything will be provided for you. Electronic devices like phones, tablets, smart watches, etc. are also not allowed. Even though you can bring snacks and water with you to the test center, you will not be allowed to take them with you into the exam room, as you’ll be asked to put them in a storage room or locker. However, you will be able to access those during your breaks. 

Am I Allowed to Bring a Calculator?

Calculators are not allowed when taking the GMAT exam, so it is best to leave it at home. In fact, it is a good idea to leave any electronic device that you will not need at home. 

Is there a Dress Code that I Should Follow?

There is no specific dress code for the test day, however, you should make sure that you dress comfortably and that you bring extra clothes in case it is cold in the exam room.

What Do I Do if My Computer Stops Working While Taking the GMAT?

If that is the case, one thing that you should not do is try to fix the computer by yourself. The best way to handle that situation is to raise your hand and ask for the administrator’s help.

What is the Best Way to Handle Disruptions While Taking the GMAT?

According to the policies, any disruptive situation that deviates from normal testing procedures will be thoroughly examined and the decision will be made on a case-to-case basis. In that case, you might be allowed to retake the exam with no additional charge or you can ask for a refund of the initial test fee. Nevertheless, there will be noises such as coughing, shifting and other small sounds that can distract you during the exam. In order to avoid this affecting your concentration drastically, spend some time practicing for the exam in an uncontrolled environment, such as a coffee shop to get yourself used to movement and sounds of others while practice focusing on your prep.

Will I be Given Something to Write on During the Exam?

You will be provided with pens and scratch paper by the test administrators once you are seated. If you are taking the online GMAT there is a on screen scratch pad and recently introduced a pre approved scratch paper option.

Do I Get to Choose the Order in Which I Take the GMAT Sections?

It is now an option for the test-takers to choose the order in which they take each section of the GMAT exam. Our instructors advise clients to take their best performing section first as they can really give it their all. You do not want to get to the section that you know you can do well at tired, after enduring the other 3 sections. 

Do We Get Breaks During the Exam?

As the GMAT exam takes a lot of time to complete, you will be allowed to go on a 5-minute break twice at scheduled intervals during that 4-hour time period. Our instructors advise you to take advantage of this time for what it is meant for, a break. Clear your mind from exam activities and try to focus on relaxing. Eating a snack is always encouraged as this will give you an energy boost, just make sure that it is the right type of snack. 

What Do I Do If I Am Not Feeling Well on Test Day?

Generally, it is not a good idea to take the GMAT exam if you’re not feeling too well on test day, as the GMAT is long and your health can potentially affect your progress and final score. If you decide to reschedule the exam 7 calendar days before your test date, you’ll only have to pay an extra $50 USD rescheduling fee and if you do so on test day, you will lose the entire test fee.

How Many Times Can I Take the GMAT Exam?

There is no limit on the number of times you can take the GMAT exam (you can take the GMAT exam up to 5 times in a 12-month period). However, it is not advised that you take it more than 3 times as it may give the wrong impression to b-schools and it’s unlikely that your scores will improve that drastically in between exams.

How Do I Send My GMAT Scores to The Schools I am Applying to?

You will get a few options regarding when to send the GMAT scores to the schools of your choice. Firstly, you can bring a list of up to 5 MBA programs on test day and your scores will be sent to those programs free of charge. Another option would be waiting to get your official score and then sending them to the schools of your choice. In this case, you’ll have to pay $28 USD for each school that your scores are sent to.

Let us know if you have any additional questions regarding your GMAT test day and one of our 770+ scoring instructors will be happy to answer them.

Taking the test in London, New York, Hong Kong or another top city? Find information about GMAT and EA test center in over 50 cities here.

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