According to a representative at the author's local branch of Chase Bank, there are in fact restrictions on the choice of digits. The following choices are prohibited. all four digits identical sequences of four consecutive ascending or descending digits, such as 6543 any sequence starting with 19 (birth years are too easy to guess) So if one of the PINs in (a) is randomly selected, what is the probability that it will be a legitimate PIN (that is, not be one of the prohibited sequences)?