# The Fundamental Counting Principle and Permutations

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The Fundamental Counting Principle and Permutations
Algebra 2: Section 12.1 The Fundamental Counting Principle and Permutations

Examples for types of problems
Experiment toss a coin roll a die toss two coins draw a card select a day of the week Sample Space head or tail 1, 2, 3, 4, 5, or 6 HH, HT, TH, or TT 52 possible outcomes Sun, Mon, Tues, Wed, Thurs, Fri, or Sat

Example You have 12 shirts, 7 pairs of pants, and 3 pairs of shoes. How many different combinations of outfits can you possibly have? You have 12 shirts, 7 pairs of pants, and 3 pairs of shoes. How many different combinations of outfits can you possibly have?

Fundamental Counting Principle
If one event occurs in m ways and another occurs in n ways, then the number of ways that both events can occur is mn. This also extends to more than two events Ex: mnp for three events that occur in m, n, and p ways

The Fundamental Counting Rule
How many possible ZIP codes are there? 10•10•10•10•10 = 100,000 How many possible ZIP codes are there if 0 can not be used for the first digit? 9•10•10•10•10 = 90,000

Example If there are five students who can receive five different scholarships, how many different ways can the five scholarships be awarded? How many different ways can the scholarships be awarded if each student can only win one scholarship?

Factorial Definition n! = n•(n-1)•(n-2)•…•3•2•1 Examples: 4! 10!
1! = ____ 0! = ____ = 4•3•2•1 = 24 = 10•9•8•7•6•5•4•3•2•1 = 3,628,800

Example The standard configuration for a New York license plate is 3 digits followed by 3 letters. How many different license plates are possible if digits and letters can be repeated? How many different license plates are possible if digits and letters cannot be repeated?

Permutations An ordering of objects
Placing a certain number of objects in a certain number of positions Notation: nPr (n things placed in r positions) Example: How many ways can you place 5 different students in 3 different chairs?

Permutation Example There are 8 different people running in the finals of the 400M dash. How many different ways can they place 1st, 2nd, and 3rd?

The Permutation Rule Example
Ex: In how many ways can a batting order be made from a team of 17 softball players?

The Fundamental Counting Rule
Extra Example: How many possible ways can three cards be drawn from a deck, without replacing them? 52•51•50 = 132,600

Permutations Examples
Extra Example: Six runners are in the first heat of the 100 meter sprint. In how many different ways can the race end? 6•5•4•3•2•1 = 720 ways In how many ways can the first three spots of the race be filled? 6•5•4 = 120 ways

Fundamental Counting Principle
If one event occurs in m ways and another occurs in n ways, then the number of ways that both events can occur is mn. This also extends to more than two events Ex: mnp for three events that occur in m, n, and p ways

Factorial Definition n! = n•(n-1)•(n-2)•…•3•2•1 Examples: 4! 10!
= 4•3•2•1 = 24 = 10•9•8•7•6•5•4•3•2•1 = 3,628,800

Permutations An ordering of objects
Placing a certain number of objects in a certain number of positions Notation: nPr (n things placed in r positions) Example: How many ways can you place 5 different students in 3 different chairs?

Example How many distinguishable permutations of the letters in MATH are there? MATH

Permutations with Repetition
The number of distinguishable permutations of n objects where one object is repeated q1 times, another is repeated q2 times, and so on is:

Permutations with Repetition Example
How many distinguishable permutations of the letters in BASKETBALL are there?

Permutations with Repetition Example
How many distinguishable permutations of the letters in MISSISSIPPI are there?