# Basic probability theory

## Abstract

The word ‘probability’ is used frequently in a loose sense implying that a certain event has a good chance of occurring. In this sense it is a qualitative or subjective measure. It is important to realize that it has a strict technical meaning and is a scientific ‘measure of chance’, i.e., it defines quantitatively the likelihood of an event or events. Mathematically it is a numerical index that can vary between zero which defines an absolute impossibility to unity which defines an absolute certainty. This scale of probability is illustrated in Figure 2.1. A philosopher might argue that the two ends of the scale do not exist. An engineer might disagree from a pragmatic viewpoint. For example, the probability that a man will live for ever is zero, and the probability that one day he will die is unity.

## Keywords

Black Ball Probability Distribution Function System Failure Venn Diagram Reliability Evaluation## Preview

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