6C4

 

  6C4     

 

  This is a mathematical expression for combinations.     

  It means the combination of six items taken four at a     

  time, also called "six choose four" sometimes.     

 

  It represents the number of different ways to select     

  four items from a group of six when the sequence of     

  selection does not matter. The value of 6C4 is 15.     

 

  An example, using smaller numbers could be 3C2 = 3.     

  The three combinations of A,B,C are AB, AC, and BC.     

_.