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: