Much of probability is based on the Fundamental Counting Principle. It says that if a first event can happen in so many ways and a second event, independent from the first event, can happen in a different number of ways, then the number of ways both events can happen is the ways for each multiplied together.
For example, suppose you go to buy a pizza and you have these choices:
Size | Crust | Topping | |
small medium large |
thin thick |
cheese sausage pepperoni combo |
Because the size, type of crust, and topping are all independent events, we can use the fundamental counting principle to determine how many different choices of pizza we could make.
number of pizzas = 3 sizes 2 crusts • 4 toppings = 3 • 2 • 4 = 24 possibilities
Buttons created at ButtonGenerator.com.