Question

John is choosing a password for an account. He has decided not to use the digit 0 or the letter m. And each letter or number can be used more than once. How many passwords of two letters followed by four digits are possible?

Answer 1

If this guy doesn't use the letter m, then the first and second characters of the password could be any of the 25 remaining letters.  So, the number of possible combinations of 2 letters is 25 times 25, or 625.  

If he doesn't use the digit 0, how many digits are left to choose from?

The first 2 characters of the password will be letters; after that there come four digits.  How many different combinations of 4 digits are there if 0 is not used?

To obtain the final result, mult. together that 625 and the number of possible combinations of digits just found above.