Question

A password question.

A password is to consist of 10 alphanumeric characters and must include
at least one lower case letter, at least one upper case letter, and at least
one digit.
(a) How many such passwords are possible?
(b) How many are possible if the password must contain at least one
lower case letter, at least one upper case letter, and at least one
digit which is immediately preceded by a letter?

Answer 1

I guess I solved the first one. 62^10 all possibility- ( no number+ no U letter+ no L letter)

Answer 2

(no numbers= L+U, no U= L+N, no L= N+U)

Answer 3

so answer seems 62^10-(52^10+36^10+30^10)

Answer 4

@amistre64