Q1) You now bought new safe:  It has key pad with 26 letters on it. 

a) If code is 4 random letters, and no letter is used more than once,  how many different possible codes are there?

b) If code is 4 random letters, and letters can be utilized multiple times, how many different possible codes are there?

c) If no letter can be utilized more than once.  Does Order Matter?

d) If manufacturer made a decision to make more secure model that uses 5 letters (no repeats) how many codes are there then?

e) If letters can be utilized multiple times and there are 5 letters, and first letter should be "A or B"   how many different codes are available?