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Probability theory is a field of mathematics that deals with the measurement of uncertain events. It is fundamental in various sectors such as finance, biology, physics, and economics. Probability theory has several basic concepts that students in maths programs must learn and understand. This article provides an in-depth understanding of these concepts, examples, and their practical applications.

Basic Concepts of Probability Theory

The following are some of the fundamental concepts of probability theory.

Random Experiment

A random experiment is defined as any experiment, which cannot be predicted with certainty. For example, rolling a dice, tossing a coin, or picking a card from a deck of cards.

Sample Space

Sample space is the set of all possible outcomes of a random experiment. It is denoted by the symbol “S”. For instance, the sample space for flipping a coin is (head, tail).

Different Types of Events

There are different types of events in probability theory, including simple events, compound events, mutually exclusive events, and independent events.

Probability of an Event (definition and formula)

Probability of an event is defined as the likelihood of that event happening. Assume that “E” is the event of a random experiment and “P(E)” is its probability. The formula for calculating the probability is, P(E) = Number of ways an event can occur/ Total number of possible outcomes.

Examples of Probability Calculations

A dice is a common example of probability calculations. If a dice is rolled randomly, then the probability of getting any number is 1/6. It means there are six possible outcomes and getting any of them has a probability of 1/6.

Equally Likely Events

Sometimes a random experiment has equally likely events. In other words, each event has the same chance of occurring. For instance, rolling a fair dice has equally likely events.

Conditional Probability

Conditional probability is the probability of an event happening given that another event has occurred. It is denoted by the symbol P(A|B).

Definition of Conditional Probability

Assume that A and B are two events such that P(B) ≠0. Then the conditional probability of A given B is defined as P(A|B) = P(A and B) / P(B)

Rules of Conditional Probability

There are two rules for conditional probability: the multiplication rule and the addition rule.

Bayes’ Theorem

Bayes’ Theorem is used to calculate the probability of an event using prior knowledge. It is used in Bayesian statistics and machine learning algorithms.

Examples of Conditional Probability Calculations

Conditional probability is widely used in daily life. For instance, the probability of a student getting good grades given that they studied hard is an example of conditional probability calculation.

Probability Distributions

Probability distributions are mathematical functions that describe the likelihood of different outcomes in a random experiment.

Introduction to Probability Distributions

Probability distribution can be either discrete or continuous.

Types of Probability Distributions

There are several types of probability distributions. These include the discrete distribution, continuous distribution, binomial distribution, Poisson distribution, and normal distribution.

Probability Distribution Function of the Discrete Distribution

Generally, the probability distribution function of a discrete distribution is the probability mass function (PMF).

Mean, Variance, and Standard Deviation of Probability Distribution

The mean, variance, and standard deviation are essential statistics that describe the characteristics of probability distributions.

Binomial and Poisson Distributions

The binomial and Poisson distributions are discrete distributions used in assessing the probabilities of distinct events.

Normal Distribution and the 68-95-99.7 Rule

The normal distribution is a continuous probability distribution that is essential in mathematical analysis and statistics. The 68-95-99.7 rule is a simple concept that is frequently used in the normal distribution.

Examples of Probability Distribution Calculations

Some examples of probability distribution calculations include determining the probability of getting a particular number on a dice with Poisson distribution calculation.

Joint Probability

Joint probability is probability theory that involves two or more events.

Definition of Joint Probability and Examples

Joint probability determines the probability of two or more events occurring simultaneously. It is denoted by the symbols P(A ∩B), P(A,B), or P(AB).

Multiplication Rule of Probability

The multiplication rule is used in calculating the joint probability of independent events.

Marginal Probability

Marginal probability is the probability of an event that can occur independent of other events.

Independence of Events

Events are independent when the occurrence of one event does not affect the probability of another event occurring. For instance, rolling a dice and tossing a coin are independent events.

Examples of Joint Probability Calculations

Joint probability is widely used in real-world situations. For instance, determining the probability of getting both heads and tails in a single coin toss.


Probability theory is a fundamental concept in mathematics with different practical applications. In summary, this comprehensive guide provides students in maths programs with the basic concepts of probability theory, including random experiment, conditional probability, probability distributions, and joint probability, among others.


Q.         What is the difference between probability and statistics?

Probability deals with the measurement of likelihood of uncertain events while statistics is the study of how to collect, analyze and interpret data.

Q.          What are some of the practical applications of probability theory?

Probability theory is widely used in various sectors such as finance, insurance, physics, and economics.

Q.          How do you calculate probability in real-world situations?

Calculate probability by dividing the number of desired outcomes by the total number of possible outcomes.

Q.          What are the most common distributions used in probability theory?

The most common distributions used in probability theory are normal, Poisson, binomial, and gamma distributions, among others.

Q.          What is the significance of Bayes’ theorem?

Bayes’ theorem is used to calculate posterior probability using prior knowledge.

Q.         How does conditional probability relate to medical testing?

Conditional probability is essential in medical testing because it helps in determining the probability of getting a particular medical condition given that a patient has exhibited some symptoms.

Q.         What is the law of large numbers in probability theory?

The law of large numbers states that the sample mean converges to the population mean as the sample size increases.

Q.          What is the central limit theorem and its significance in probability theory?

The central limit theorem states that as the sample size increases, the distribution of the sample means approaches a normal distribution. It is significant in probability theory because it provides a theoretical foundation for decision-making processes.