### Introduction

When we require the probability of two events occurring simultaneously or the probability of one or the other or both of two events occurring then we need probability laws to carry out the calculations. For example, if a traffic management engineer looking at accident rates wishes to know the probability that cyclists and motorcyclists are injured during a particular period in a city, he or she must take into account the fact that a cyclist and a motorcyclist might collide. (Both events can happen simultaneously.)

#### Prerequisites

• understand the ideas of sets and subsets
• understand the concepts of probability and events

#### Learning Outcomes

• state and use the addition law of probability
• define the term independent events
• state and use the multiplication law of probability
• understand and explain the concept of conditional probability