Combination Formulas

Factorial of n,n! :

The Combinations formula:
  
Important formulas on Combinations:

  1. nc0 = 1

  2. ncn = 1

  3. ncr = ncn-r

  4. The number of groups (combinations) of n different things taking any number at a time is:
    nc0 + nc1 + nc2 +….. ncn = 2n – 1
  5. The number of ways (alternatively groups or combinations) in which n things can be divided into p things and q things is
  6. The number of ways (alternatively groups or combinations) in which 3n can be divided equally into three distinct groups each having n things is
  7. The number of ways (alternatively groups or combinations) in which 3n can be divided equally into three identical groups each having n things is