6.4 notes permutations vs combinations.doc
This preview shows half of the first page. to view the full 1 pages of the document.
Section 6.4: Combinations vs. Permutations
•Permutation of n objects not all of which are distinct
•Previously, we had n objects all of which are different
•In this case, you divid out all repetitions in set
◦n!/ n(1)!, n(2)!....
•Combinations: number of ways of selecting r objects from n objects
◦order is not important
•C(n,r) = n!/ r! (n-r)! VS. P(n,r) = n!/ (n-r)!
- numbers - groups
- words - committees
•ex: select 3 phones from 100 = combination
•ex: 4 mutual funds from 8 can be grouped how many ways?
•ex: 6 candidates can be arranged how many ways on a ballot?
◦P(6,6) OR 6!
•“or” = + = union
•“and” = X = intersection
You're Reading a Preview
Unlock to view full version