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)!

Permutations Combinations

- numbers - groups

- words - committees

- schedule

-arrangement

-contest

-codes

•ex: select 3 phones from 100 = combination

•ex: 4 mutual funds from 8 can be grouped how many ways?

◦C(8,4)

•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