This **probability calculator** calculates the normal probability for single and multiple events, which is the chance that a specific event could take place. There is more information about the calculation method right after the tool.

## Understanding what is a probability

Probability is defined as the chance that a certain event could take place. Since it measures the likeliness that a certain thing will occur, it is a theory that is used in many day by day decisions.

It can be expressed with a number (e.g 0.5), or percentage (e.g 50%=0.5) or with a word expression such as likely, unlikely, possible.

## How to calculate probabilities?

The algorithm of this *probability calculator* is based on the equations provided below:

- Probability formulas for
**single**event:

- Probability that A take place is P(A) = n(A) / n(T).

- Probability that A does not occur is P(A’)= 1 - P(A).

- Probability formulas for
**multiple event**:

- Probability for A to happen is P(A)= n(A) / n(T).

- Probability that A does not occur is P(A’)= 1 - P(A).

- Probability that B take place is P(B)= n(B) / n(T).

- Probability that B does not happen is P(B’)= 1 - P(B).

- Probability that both events (A and B) occur is P(A ∩ B)= P(A) x P(B).

- Probability that either A or B occurs is P(A ∪ B)= P(A) + P(B) - P(A ∩ B).

- Conditional Probability is P(A | B)= P(A ∩ B) / P(B).

The notations used are:

n(A)= the no. of favorable A event

n(B)= the no. of favorable B event

n(T)= the total no. of events

11 Apr, 2015