21.1 Introduction21.2 Population and sample, representation of data, mean, variance and standard deviation21.3 Random systems and probability21.4 Addition law of probability21.5 Repeated trials, outcomes, and probabilities21.6 Repeated trials and probability trees21.7 Conditional probability and probability trees21.8 Application of the probability laws to the probability of failure of an electrical circuit21.9 Statistical modelling21.10 The normal distribution21.11 The exponential distribution21.12 The binomial distribution21.13 The Poisson distribution21.14 Summary21.15 Exercises