Combination Formula
A formula for the number of possible
combinations of r objects
from a set of n objects. This
is written in any of the ways shown below.
All forms are read aloud "n choose r."
Formula: 


Note: , where _{n}P_{r} is the formula for permutations of n objects taken r at a time. 
Example: 
How many different committees of 4 students can be chosen from a group of 15?

Answer: 
There are possible combinations of 4 students from a set of 15. 

There are 1365 different committees. 
See
also
Permutation, binomial
coefficient,
factorial
