Nothing in life is certain and we may even say that nothing in the universe is certain. We can adapt in such a world by uderstanding how to deal with uncertainties and learning how to make decisions in the light of chance phenomena. The systematic study of chance or random phenomena is called probability theory. Probability theory becomes important when we do not have enough information to describe a situation completely. Using the partial information at our disposal we cannot predict precisely what will occur, but we can predict the chances or the probabilities that different alternatives have of occurring. In this series of four lectures we will discuss various problems in basic probability theory. Some of these problems such as computing odds in games of chance are mainly recreational while others such as the accuracy of tests for AIDS have serious implications.