Permutation lock:- A permutation is an ordered combination. ( a lock problem) (multiplication priciple)

it can have 2 types:- 

1) Repetition Allowed :- When  a thing has 3 different types, we have N choices each times. Hence the permutation will be =N*N*N

2) No Repetition :- N factorial / (N-r) factorial

Combination:- is counting of selections that we make for N objects whereas permutation is counting the number of arrangements of N objects 

care about selections