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How to Solve Probability Questions on the GRE Exam

The GRE’s Quantitative Reasoning section includes questions on probability. This can be a difficult topic for some test-takers, but with the right preparation, it can be mastered. In this blog post, we will discuss what probability is and how to solve probability questions on the GRE exam. We will provide examples of word problems as well to help your understanding of the concept.

Probability is a measure of the likelihood that an event will occur. We can express probability as a number between 0 and 1, where 0 means an event is impossible and 1 means an event is certain to happen. For example, the probability of flipping a coin and getting heads is 0.5 or 50%.

In many probability questions, you’ll be asked about mutually exclusive events. Mutually exclusive events are events that, you guessed it, can never happen together. The individual probabilities for these events will always sum up to 100%. For instance, if you flip a normal coin, you’ll have a 50% chance of heads and a 50% chance of tails. 50% + 50% = 100%. And that makes sense since the outcome can only be one or the other.

There are two types of probability problems that you may see on the GRE: marginal probability and joint probability. In a marginal probability problem, you are asked to find the probability of one event occurring. For example, if you roll a die, what is the probability of rolling a 4? The answer is 1/6 or 16.67%.

In a joint probability problem, you are asked to find the probability of two events occurring. For example, if you roll a die, what is the probability of rolling a 4 and a 3? The answer is 1/6 x 1/6 = 1/36 or 2.78%.

Now let’s try to solve some word problems.

Example 1: 

If a fair coin is flipped three times, what is the probability of getting exactly two heads?

To solve this problem, we need to find the probability of getting two heads and one tail, which is a joint probability. Since the probability of getting heads is 1/2 or 50% and you flip the coin three times, you multiply 1/2 by itself three times:

1/2 x 1/2 x 1/2 = 1/8 or 12.5%.

So the probability of getting two heads and one tail is 1/8 or 12.5%.

Example 2: 

A card is drawn from a standard deck of 52 cards. What is the probability of drawing an ace or a heart?

There are four aces in a deck of cards, so the probability of drawing an ace is 4/52 or 7.69%. There are thirteen hearts in a deck of cards, so the probability of drawing a heart is 13/52 or 25%. The probability of drawing an ace or a heart is the sum of the probabilities of those two events occurring:

4/52 + 13/52 = 17/52 or 32.69%

With these tips and examples, you should be well on your way to solving probability questions on the GRE exam. For more practice, check out Achievable’s GRE prep course. Our course includes practice questions and full-length practice exams to help you master everything you need to know for the GRE. Good luck with your exam!

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