Permutation and Combination

Permutation means when the order is important.

Formula: nPr=n!/(n-r)!

Combination means when the order is not important.

Formula: nCr=n!/(n-r)!r!

Example 1.
In how many ways can 8 CD’s be arranged on a shelf?

Since order is important, you use permutation

Example 2:

In how many ways can a sorority of 20 members select a president, vice president and treasury, assuming that the same person cannot hold more than one office.

Order is important