S.5 math's Q on Probability

2. The licence pates of cars consist of 2 upper case letters followed by 4 digits,
in which the first digit cannot be '0'.

(a) If the letter ' I ' and ' O' cannot be used and the digits cannot be all the same, then how many different license plates are posible? (Anwser : 5178816)



3. Suppose each user on a computer system requires a password of 6
characters. Each character can be a lower case letter or a digit. If the
password must contain at least one digit, find the number of possble
passwords. (Answer : 1867866560)