Key Equations
number of permutations of n distinct objects taken r at a time | P(n,r)=n!(n−r)! |
number of combinations of n distinct objects taken r at a time | C(n,r)=n!r!(n−r)! |
number of permutations of n non-distinct objects | n!r1!r2!…rk! |
Binomial Theorem | (x+y)n=n∑k−0(nk)xn−kyk |
(r+1)th term of a binomial expansion | (nr)xn−ryr |
Key Concepts
- If one event can occur in m ways and a second event with no common outcomes can occur in n ways, then the first or second event can occur in m+n ways.
- If one event can occur in m ways and a second event can occur in n ways after the first event has occurred, then the two events can occur in m×n ways.
- A permutation is an ordering of n objects.
- If we have a set of n objects and we want to choose r objects from the set in order, we write P(n,r).
- Permutation problems can be solved using the Multiplication Principle or the formula for P(n,r).
- A selection of objects where the order does not matter is a combination.
- Given n distinct objects, the number of ways to select r objects from the set is C(n,r) and can be found using a formula.
- A set containing n distinct objects has 2n subsets.
- For counting problems involving non-distinct objects, we need to divide to avoid counting duplicate permutations.
- (nr) is called a binomial coefficient and is equal to C(n,r).
- The Binomial Theorem allows us to expand binomials without multiplying.
- We can find a given term of a binomial expansion without fully expanding the binomial.
Glossary
Addition Principle if one event can occur in m ways and a second event with no common outcomes can occur in n ways, then the first or second event can occur in m+n ways
binomial coefficient the number of ways to choose r objects from n objects where order does not matter; equivalent to C(n,r), denoted (nr)
binomial expansion the result of expanding (x+y)n by multiplying
Binomial Theorem a formula that can be used to expand any binomial
combination a selection of objects in which order does not matter
Fundamental Counting Principle if one event can occur in m ways and a second event can occur in n ways after the first event has occurred, then the two events can occur in m×n ways; also known as the Multiplication Principle
Multiplication Principle if one event can occur in m ways and a second event can occur in n ways after the first event has occurred, then the two events can occur in m×n ways; also known as the Fundamental Counting Principle
permutation a selection of objects in which order matters
Candela Citations
- Revision and Adaptation. Provided by: Lumen Learning. License: CC BY: Attribution
- College Algebra. Authored by: Abramson, Jay et al.. Provided by: OpenStax. Located at: http://cnx.org/contents/9b08c294-057f-4201-9f48-5d6ad992740d@5.2. License: CC BY: Attribution. License Terms: Download for free at http://cnx.org/contents/9b08c294-057f-4201-9f48-5d6ad992740d@5.2
- Precalculus. Authored by: OpenStax College. Provided by: OpenStax. Located at: http://cnx.org/contents/fd53eae1-fa23-47c7-bb1b-972349835c3c@5.175:1/Preface. License: CC BY: Attribution