Permutation and Combination

Permutation and combination are ways to solve problems that ask about the order of things. Most of the will ask in how many ways are possible if oder is not important or is important. These problems are just problems of order involving choices. If you follow the formula you will almsot always likely get the right answer.

Permutation: where the order of selection is important
Combination: where the order of the selction in not important

Formulas:
Permutation- n!/(n-r)!
Combination- n!/(n-r)! r!

*There is also a type of permutation with repetition. It means the order is importatn but you may have of or more of a type of item. When you have a problem like this you use the formula:
n!/n1! n2! n3!........

EX1 5P2
means 5 Permutation of 2
A. plug into formula and get 5!/3!
you get 20

EX2 There are 2 spots in a dance. A teacher will pick form her 6 students to perform that number. List all possible ways the spots can be filled.
A. It is combination because they have no specifics about the spots.
B. Use formula and plug in 6!/4! 2! = 10