Assume that each password is created I according to Exercise 13.3. If passwords are independent and 10 passwords are I created:
a. What is the expected total number of letters which are used?
b. What is the standard deviation of the total number of letters which are used?
c. What is the probability that at least 2 of these passwords are identical?
d. If 100 passwords are created, what is the probability that at least 2 of the passwords are identical?