1Permutation means arrangement
Fundamental principles of counting
If a work can be done in m ways and the either can be done in n ways, then the no .of ways in which both the works can be done is m×n ways.
But if they are done I depend on each other that is doing of one does not affect the other, then it is m+n.
The no of ways in which n different things can be arranged is n! Which is equal to
n!=n ×(n-1)×.....×2×1.
The no. of ways in which r things out of n things can be arranged is
n^P^r = n!/(n-r)!.
If any particular object is repeated p, q.. times then the result is divided by p! q!... respectively to get the desired permutation.
