Animated ChalkboardFundamental Counting Principle

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 Pizza slice
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


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Last Updated: 8/1/2007
K. A. Shearer 2007
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