Assuming digits, prob. of digit is 1/10
Assuming letters, prob of letter is 1/52
Assuming lowercase or uppercase, prob of letter is 1/26
For example, the password is 3fds66
You know it has only lowercase letters.
You know the amount of letters and numbers.
P(guessing the password)= 1/10*1/26*1/26*1/26*1/10*1/10=1/1757600
