letters are permitted, how many possible license plates are there? (b) If no letters and no digits are repeated, how many license plates are possible?...

(a) If no repetitions of letters are permitted, how many possible license plates are there? (b) If no letters and no digits are repeated, how many license plates are possible? Problem 35.6 A combination lock has 40 numbers on it. (a) How many different three-number combinations can be made? (b) How many different combinations are there if the numbers must be all different? Problem 35.7 (a) Miss Murphy wants to seat 12 of her students in a row for a class picture. How many different seating arrangements are there?