The Counting Principle
The Fundamental Counting Principle offers another way of calculating how many possible outcomes of an event.
If there are two or more variables (stages of activity) the total number of possible outcomes is the product of the number of possible outcomes for each stage of the activity.
Example: A clothing store sells shirts in eight different sizes. For each size, there is a choice of five different colors and for each color; there is a choice of six different patterns. If the store has one of each available type of shirt, how many different shirts does the store have?
In the above example there are three variables or stages so I would multiply the 8 choices of sizes by the 5 colors and then the 6 patterns to determine that there are 240 possible outcomes or different shirts.
If I then wanted to know the number of size 6, pink or blue, stripes= 1 ∙ 2 ∙ 1 favorable outcomes so the P(size 6, pink or blue, stripes) =