Posted by Diana on Wednesday, July 29, 2009 at 6:53pm.
how many 4 character license plates are possible with 2 letters of the alphabet followed by 2 digits, it repetitions are allowed?
if repetitions are not allowed?

math  MathMate, Wednesday, July 29, 2009 at 7:12pm
Assuming all 26 letters are used, there is a choice of 25 letters for the first character, 26 for the second, 10 for the third, and 9 for the fourth.
The total number is the product of the four numbers. 
math  MathMate, Wednesday, July 29, 2009 at 7:13pm
If repetitions are allowed, the choies are 26,26,10,10.