## How to find Probability of an event?

Forum for OpenSees users to post questions, comments, etc. on the use of the OpenSees interpreter, OpenSees.exe

Moderators: silvia, selimgunay, Moderators

shaunmurphy
Posts: 1
Joined: Sun Apr 12, 2020 6:07 am

### How to find Probability of an event?

Probability is the extent or likelihood of an event to happen. It can also be defined as a kind of ratio, where we focus on the chances of a certain outcome compared to all other possible outcomes. For instance, the possibility of getting a four when we roll a die? Now, if we consider the ratio aspect in mind;
Probability= P = Desired number of outcome/ All possible outcomes
Here, we know that a dice has 6 sides, so the possibility of getting a 4 is 1/6.
In this article we will discuss all the possible methods to deal with outcomes of an event.
When we talk about finding the probability of an event, we must know how to deal with dependent and independent events.
Independent Events:
The two events are considered independent, when the possible outcome of the first event has no impact on the outcome of the 2nd event.
In order to calculate the end result of two independent events, we multiply the probability of first with that of the second event.
For example, if one has to find the possibility of getting 6 on rolling two dice:
Probability with two dice = 1/6 * 1/6 = 1/36
Dependent Events:
We say two events are dependent, if the outcome of one event has an effect on the outcome of another.
For example, the chances of getting 2 black cards from a deck of cards:
A deck consists of 52 cards in total, 26 red and 26 black cards, we will find it as;
P (black) = 26/52 = 1/2, now the chances of having a 2nd black card are as follows:
P (2nd black) = 25/51 (as one card was already drawn from the deck)
Now multiply both, P= 1/2 * 25/51 = 25/102
Methods of finding Probability:
There are many ways to calculate the possible outcome, some of these methods are listed below;
The classical one:
The method we discussed at the start is the classical way to calculate the probability. Here all the possible results are known, and there are exactly equal chances of getting each result. For instance, we mentioned the example of getting a four out of six possibilities in rolling a dice. It is as likely to get a four as one or any other number from 1 to 6.
The Relative Frequency:
This technique is utilized in that case, when we don’t have the advanced info of all other results or outcomes. Moreover, in case where the likelihood of occurrence is different. It implies comparable statistics from a preceding but similar instance. An example of how the relative frequency technique would be applied; is a shop owner, placing orders based on the data of previous year's deals or sales.
The Subjective Method:
This method is needed in those cases, where we don’t have the advance knowledge of all the probable outcomes, all outcomes aren’t likely equal. Along with these situations, when we don’t even have prior statistical data. This technique is completely based on the opinions, previous exposures or experience, which is the reason why we call it the subjective method. After you are done with the predictions, you can always get better by refining the data and trying again.
Online Tools:
Last but not the least, giving the digital technology a try. There are a bunch of online websites available, where you can find these gizmos. The best thing about these smart tools is the precision. If you want to get more accurate info, without wasting time on calculation, try tools such as <a href="https://www.calculatored.com/math/proba ... robability calculator</a> or <a href="https://www.calculatored.com/math/algeb ... ombination calculator</a>.
In the end, I hope this article will assist you in understanding the core concepts of finding the probability. Good luck!