Factorials, Combinations and Permutations Calculators
by Joe McDonald
Factorials  Combinations  Permutations 
A factorial is denoted using an ! symbol. For example...






As you can see, 10!, pronounced 10 factorial, is a large number. What about 20! or 100!?  
Most calculators including the TI 's series will only calculate factorials up to 69!  


Other important facts....  
n! = n(n  1)(n 2) · · ·1 where n is an integer greater than 0  



Example
There are n! distinct arrangement of n distinct objects. If 3 people race, there are 3! = 6 different outcomes. If you want to arrange 6 different books on a shelf, there are 6! = 720 diiferent arrangements.
An alternate form for combinations  unordered 
Notice C(7,4) = C(7,3) = 35 Why? 
An alternate form for permutations  ordered 
Notice P(7,4)
= 840 but P(7,3) = 210 