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.Formula:  
Note: , where _{n}P_{r} is the formula for permutations of nobjects taken r at a time.  
Example:  How many different committees of 4 students can be chosen from a group of 15?  
Answer:  
There are 1365 different committees.
