6 How many 6symbol computer passwords can be formed if the f

6. How many 6-symbol computer passwords can be formed if the first two symbols are letters (either upper or lower case) and the rest of the symbols are digits? (Letters and digits may be repeated.)

Solution

Here

either upper case or lower case letters can be used,
i presume they are to be treated as distinct, so 52 symbols for letters are available,

and the rest of four symbols are digits.
   so

        52*52*10*10*10*10 =27,040,000