Introduction

Many probability questions arise out of simple curiosity about the world we experience. What is the probability that a randomly selected batter on a Major League Baseball team is a switch-hitter (bats left or right depending on the situation)? What is the probability that the next video uploaded to YouTube is in Spanish? What is the probability that your first roll of the dice is a 12 when playing a game of Monopoly? What is the probability that all children in a 4-child family are girls? What is the probability that you get at least 7 out of 10 correct on a multiple-choice pop quiz if you guess at each answer?

In this chapter, we will explore situations like these in which random phenomena have discrete probability models. A discrete probability model arises when a random phenomenon has only a fixed number of possible outcomes, as in recording how a Major League baseball player bats (left, right, or both) or observing the number of girls in a 4-child family (0, 1, 2, 3, or 4).