Question

"a computer system requires that passwords contain at least one digit. if "seven" characters are generated at random, and each is equally likely to be any of the 26 letters or 10 digits, what is the probability that a valid password will be generated?"

Answer 1

There are 36^7 different passwords available, incluiding ones that have repeated characters, are sequential characters, or are all the same letter or digit. Of these 26^7 are invalid. the probability of obtaining a valid password is

... 1 - 26^7/36^7 ≈ 0.8975