PROBABILITY

 DEFINITION OF PROBABILITY

The probability of a certain event A happening in sample space S is given by the ratio between the number of cases favorable to the event (nA) and the total number of possible cases (n):

BASIC PROBABILITY RULES

1. Probability Variation Field

The probability of an event A happening is a number between 0 and 1:

2. Probability of the Sample Space

Sample space S has probability equal to 1:

3. Probability of an Empty Set

The probability of an empty set (f) occurring is null:

4. Probability Variation Field

The probability of event A, event B or both happening can be calculated as follows:

5. Probability of a Complementary Event

If Ac is A’s complementary event, then:

6. Probability Multiplication Rule for Independent Events

If A and B are two independent events, the probability of them happening together is equal to the product of their individual probabilities: