Combinations

• A Combination is a distinct group of objects without regard to their arrangement.
  • There is no rank or position.
  • There is no difference in value.
  • Order does not matter.
• For the set {a,b,c} write all of the
  • Two letter permutations.
  • Two letter combinations.
• The formula for r objects chosen from n objects is
  • $_nC_r = \frac{ n!}{ (n-r)! r!}$
• Do some problems.