13. A company has its employees choose a password which consists of 7 characters: 2 letters, followed by 2 symbols, followed by 3 digits. There are a total of 11 symbols that the employees can choose from. Letters, symbols and digits cannot be repeated. How many possible passwords are there?

15. Suppose your bank requires that you create a 4-digit Personal Identification Number (PIN) to access your account. Your PIN can use only the digits 0 9 and digits can be repeated; however the first digit cannot be 0. How many possible PINs are there?

17. A radio station is known by its call-letters which are 4 letters which must start with the letter K. How many possible station names are there if the letters can be repeated?

19. Current Texas automobile license tags consist of 2 letters, followed by a non-zero number, followed by a letter, followed by 3 numbers. The letters I and O are never used on license tags. Letters and digits can be repeated. How many possible automobile tags are there?

21. A serial number for a dishwasher consists of 3 letters, followed by 7 digits. The letters O, I and Q are not used but all digits can be used. How many serial numbers are there if: A. Letters can be repeated but digits cannot be repeated?

B. Digits can be repeated but letters cannot be repeated?

C. Both letters and digits can be repeated?

D. Neither letters nor digits can be repeated?