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Stats. Section 3.7 Notes. Fundamental Counting Rule. For a sequence of two events in which the first event can occur in m ways and the second event can occur in n ways, the events together can occur a total of m x n ways. Example.
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Stats Section 3.7 Notes
Fundamental Counting Rule • For a sequence of two events in which the first event can occur in m ways and the second event can occur in n ways, the events together can occur a total of m x n ways.
Example • How many license plates in the state of Ohio can be made (excluding vanity plates), if the plate consists of three letters from the alphabet followed by 4 single digit numbers? • 26 x 26 x 26 x 10 x 10 x 10 x 10 = 175,760,000 plates
Factorial • The factorial symbol ! Denotes the product of decreasing positive whole numbers. For example:
Factorial Rule • A collection of n different items can be arranged in order n! different ways. • There are 28 desks in this room. There are 28! = 304,888,344,600,000,000,000,000,000,000 different ways to arrange them.
Permutations Rule (when all items are all different) • The number of permutations (or sequences) of r items selected from n available items (without replacement) is:
Permutation requirements • 1. We must have a total of n different items available. (This rule does not apply if some of the items are identical) • 2. We must select r of the n items. • 3. We must consider rearrangements of the same items to be different sequences. Basically, the order of the items is important. ABC is not the same as BAC.
Combination Rule • The number of combinations of r items selected from n different items is:
Combination requirements • 1. We must have a total of n different items available. • 2. We must select r of the n items (without replacement) • 3. We must consider rearrangements of the same items to be the same. Basically, the order of the items is not important. ABC and BAC are the same thing.